diff --git a/src/Symfony/Component/Translation/Catalogue/AbstractOperation.php b/src/Symfony/Component/Translation/Catalogue/AbstractOperation.php
index 919bab8fff97..e482aee769f4 100644
--- a/src/Symfony/Component/Translation/Catalogue/AbstractOperation.php
+++ b/src/Symfony/Component/Translation/Catalogue/AbstractOperation.php
@@ -88,7 +88,7 @@ public function getDomains()
     /**
      * {@inheritdoc}
      */
-    public function getMessages($domain)
+    public function getMessages(string $domain)
     {
         if (!\in_array($domain, $this->getDomains())) {
             throw new InvalidArgumentException(sprintf('Invalid domain: %s.', $domain));
@@ -104,7 +104,7 @@ public function getMessages($domain)
     /**
      * {@inheritdoc}
      */
-    public function getNewMessages($domain)
+    public function getNewMessages(string $domain)
     {
         if (!\in_array($domain, $this->getDomains())) {
             throw new InvalidArgumentException(sprintf('Invalid domain: %s.', $domain));
@@ -120,7 +120,7 @@ public function getNewMessages($domain)
     /**
      * {@inheritdoc}
      */
-    public function getObsoleteMessages($domain)
+    public function getObsoleteMessages(string $domain)
     {
         if (!\in_array($domain, $this->getDomains())) {
             throw new InvalidArgumentException(sprintf('Invalid domain: %s.', $domain));
@@ -153,5 +153,5 @@ public function getResult()
      *
      * @param string $domain The domain which the operation will be performed for
      */
-    abstract protected function processDomain($domain);
+    abstract protected function processDomain(string $domain);
 }
diff --git a/src/Symfony/Component/Translation/Catalogue/MergeOperation.php b/src/Symfony/Component/Translation/Catalogue/MergeOperation.php
index d2f4abd13ff4..2a23e8599093 100644
--- a/src/Symfony/Component/Translation/Catalogue/MergeOperation.php
+++ b/src/Symfony/Component/Translation/Catalogue/MergeOperation.php
@@ -27,7 +27,7 @@ class MergeOperation extends AbstractOperation
     /**
      * {@inheritdoc}
      */
-    protected function processDomain($domain)
+    protected function processDomain(string $domain)
     {
         $this->messages[$domain] = [
             'all' => [],
diff --git a/src/Symfony/Component/Translation/Catalogue/OperationInterface.php b/src/Symfony/Component/Translation/Catalogue/OperationInterface.php
index 87d888efb76e..9ffac88d28d4 100644
--- a/src/Symfony/Component/Translation/Catalogue/OperationInterface.php
+++ b/src/Symfony/Component/Translation/Catalogue/OperationInterface.php
@@ -44,29 +44,23 @@ public function getDomains();
     /**
      * Returns all valid messages ('all') after operation.
      *
-     * @param string $domain
-     *
      * @return array
      */
-    public function getMessages($domain);
+    public function getMessages(string $domain);
 
     /**
      * Returns new messages ('new') after operation.
      *
-     * @param string $domain
-     *
      * @return array
      */
-    public function getNewMessages($domain);
+    public function getNewMessages(string $domain);
 
     /**
      * Returns obsolete messages ('obsolete') after operation.
      *
-     * @param string $domain
-     *
      * @return array
      */
-    public function getObsoleteMessages($domain);
+    public function getObsoleteMessages(string $domain);
 
     /**
      * Returns resulting catalogue ('result').
diff --git a/src/Symfony/Component/Translation/Catalogue/TargetOperation.php b/src/Symfony/Component/Translation/Catalogue/TargetOperation.php
index 22aa9a391117..249a521bb8d0 100644
--- a/src/Symfony/Component/Translation/Catalogue/TargetOperation.php
+++ b/src/Symfony/Component/Translation/Catalogue/TargetOperation.php
@@ -28,7 +28,7 @@ class TargetOperation extends AbstractOperation
     /**
      * {@inheritdoc}
      */
-    protected function processDomain($domain)
+    protected function processDomain(string $domain)
     {
         $this->messages[$domain] = [
             'all' => [],
diff --git a/src/Symfony/Component/Translation/DataCollectorTranslator.php b/src/Symfony/Component/Translation/DataCollectorTranslator.php
index 37dd5b4af32f..80e9b0077009 100644
--- a/src/Symfony/Component/Translation/DataCollectorTranslator.php
+++ b/src/Symfony/Component/Translation/DataCollectorTranslator.php
@@ -74,7 +74,7 @@ public function getLocale()
     /**
      * {@inheritdoc}
      */
-    public function getCatalogue($locale = null)
+    public function getCatalogue(string $locale = null)
     {
         return $this->translator->getCatalogue($locale);
     }
diff --git a/src/Symfony/Component/Translation/Dumper/CsvFileDumper.php b/src/Symfony/Component/Translation/Dumper/CsvFileDumper.php
index bfa8db61adef..32accb66bdde 100644
--- a/src/Symfony/Component/Translation/Dumper/CsvFileDumper.php
+++ b/src/Symfony/Component/Translation/Dumper/CsvFileDumper.php
@@ -26,7 +26,7 @@ class CsvFileDumper extends FileDumper
     /**
      * {@inheritdoc}
      */
-    public function formatCatalogue(MessageCatalogue $messages, $domain, array $options = [])
+    public function formatCatalogue(MessageCatalogue $messages, string $domain, array $options = [])
     {
         $handle = fopen('php://memory', 'r+b');
 
@@ -43,11 +43,8 @@ public function formatCatalogue(MessageCatalogue $messages, $domain, array $opti
 
     /**
      * Sets the delimiter and escape character for CSV.
-     *
-     * @param string $delimiter Delimiter character
-     * @param string $enclosure Enclosure character
      */
-    public function setCsvControl($delimiter = ';', $enclosure = '"')
+    public function setCsvControl(string $delimiter = ';', string $enclosure = '"')
     {
         $this->delimiter = $delimiter;
         $this->enclosure = $enclosure;
diff --git a/src/Symfony/Component/Translation/Dumper/DumperInterface.php b/src/Symfony/Component/Translation/Dumper/DumperInterface.php
index 9965e8091f86..3cd9b905cb22 100644
--- a/src/Symfony/Component/Translation/Dumper/DumperInterface.php
+++ b/src/Symfony/Component/Translation/Dumper/DumperInterface.php
@@ -27,5 +27,5 @@ interface DumperInterface
      * @param MessageCatalogue $messages The message catalogue
      * @param array            $options  Options that are used by the dumper
      */
-    public function dump(MessageCatalogue $messages, $options = []);
+    public function dump(MessageCatalogue $messages, array $options = []);
 }
diff --git a/src/Symfony/Component/Translation/Dumper/FileDumper.php b/src/Symfony/Component/Translation/Dumper/FileDumper.php
index 07eb78e9ebc1..e257e722461d 100644
--- a/src/Symfony/Component/Translation/Dumper/FileDumper.php
+++ b/src/Symfony/Component/Translation/Dumper/FileDumper.php
@@ -37,7 +37,7 @@ abstract class FileDumper implements DumperInterface
      *
      * @param string $relativePathTemplate A template for the relative paths to files
      */
-    public function setRelativePathTemplate($relativePathTemplate)
+    public function setRelativePathTemplate(string $relativePathTemplate)
     {
         $this->relativePathTemplate = $relativePathTemplate;
     }
@@ -45,7 +45,7 @@ public function setRelativePathTemplate($relativePathTemplate)
     /**
      * {@inheritdoc}
      */
-    public function dump(MessageCatalogue $messages, $options = [])
+    public function dump(MessageCatalogue $messages, array $options = [])
     {
         if (!\array_key_exists('path', $options)) {
             throw new InvalidArgumentException('The file dumper needs a path option.');
@@ -87,13 +87,9 @@ public function dump(MessageCatalogue $messages, $options = [])
     /**
      * Transforms a domain of a message catalogue to its string representation.
      *
-     * @param MessageCatalogue $messages
-     * @param string           $domain
-     * @param array            $options
-     *
      * @return string representation
      */
-    abstract public function formatCatalogue(MessageCatalogue $messages, $domain, array $options = []);
+    abstract public function formatCatalogue(MessageCatalogue $messages, string $domain, array $options = []);
 
     /**
      * Gets the file extension of the dumper.
diff --git a/src/Symfony/Component/Translation/Dumper/IcuResFileDumper.php b/src/Symfony/Component/Translation/Dumper/IcuResFileDumper.php
index 48d0befdf941..e04ae3a7df79 100644
--- a/src/Symfony/Component/Translation/Dumper/IcuResFileDumper.php
+++ b/src/Symfony/Component/Translation/Dumper/IcuResFileDumper.php
@@ -28,7 +28,7 @@ class IcuResFileDumper extends FileDumper
     /**
      * {@inheritdoc}
      */
-    public function formatCatalogue(MessageCatalogue $messages, $domain, array $options = [])
+    public function formatCatalogue(MessageCatalogue $messages, string $domain, array $options = [])
     {
         $data = $indexes = $resources = '';
 
@@ -82,7 +82,7 @@ public function formatCatalogue(MessageCatalogue $messages, $domain, array $opti
         return $header.$root.$data;
     }
 
-    private function writePadding($data)
+    private function writePadding(string $data)
     {
         $padding = \strlen($data) % 4;
 
@@ -91,7 +91,7 @@ private function writePadding($data)
         }
     }
 
-    private function getPosition($data)
+    private function getPosition(string $data)
     {
         return (\strlen($data) + 28) / 4;
     }
diff --git a/src/Symfony/Component/Translation/Dumper/IniFileDumper.php b/src/Symfony/Component/Translation/Dumper/IniFileDumper.php
index 45ff9614b146..93c900a4a9fb 100644
--- a/src/Symfony/Component/Translation/Dumper/IniFileDumper.php
+++ b/src/Symfony/Component/Translation/Dumper/IniFileDumper.php
@@ -23,7 +23,7 @@ class IniFileDumper extends FileDumper
     /**
      * {@inheritdoc}
      */
-    public function formatCatalogue(MessageCatalogue $messages, $domain, array $options = [])
+    public function formatCatalogue(MessageCatalogue $messages, string $domain, array $options = [])
     {
         $output = '';
 
diff --git a/src/Symfony/Component/Translation/Dumper/JsonFileDumper.php b/src/Symfony/Component/Translation/Dumper/JsonFileDumper.php
index 2af8231bd6fd..c6700ae153f1 100644
--- a/src/Symfony/Component/Translation/Dumper/JsonFileDumper.php
+++ b/src/Symfony/Component/Translation/Dumper/JsonFileDumper.php
@@ -23,7 +23,7 @@ class JsonFileDumper extends FileDumper
     /**
      * {@inheritdoc}
      */
-    public function formatCatalogue(MessageCatalogue $messages, $domain, array $options = [])
+    public function formatCatalogue(MessageCatalogue $messages, string $domain, array $options = [])
     {
         $flags = $options['json_encoding'] ?? JSON_PRETTY_PRINT;
 
diff --git a/src/Symfony/Component/Translation/Dumper/MoFileDumper.php b/src/Symfony/Component/Translation/Dumper/MoFileDumper.php
index 27be16d573f4..955f7e66b9f4 100644
--- a/src/Symfony/Component/Translation/Dumper/MoFileDumper.php
+++ b/src/Symfony/Component/Translation/Dumper/MoFileDumper.php
@@ -24,7 +24,7 @@ class MoFileDumper extends FileDumper
     /**
      * {@inheritdoc}
      */
-    public function formatCatalogue(MessageCatalogue $messages, $domain, array $options = [])
+    public function formatCatalogue(MessageCatalogue $messages, string $domain, array $options = [])
     {
         $sources = $targets = $sourceOffsets = $targetOffsets = '';
         $offsets = [];
diff --git a/src/Symfony/Component/Translation/Dumper/PhpFileDumper.php b/src/Symfony/Component/Translation/Dumper/PhpFileDumper.php
index e77afc2fbfde..6163b5297c10 100644
--- a/src/Symfony/Component/Translation/Dumper/PhpFileDumper.php
+++ b/src/Symfony/Component/Translation/Dumper/PhpFileDumper.php
@@ -23,7 +23,7 @@ class PhpFileDumper extends FileDumper
     /**
      * {@inheritdoc}
      */
-    public function formatCatalogue(MessageCatalogue $messages, $domain, array $options = [])
+    public function formatCatalogue(MessageCatalogue $messages, string $domain, array $options = [])
     {
         return "<?php\n\nreturn ".var_export($messages->all($domain), true).";\n";
     }
diff --git a/src/Symfony/Component/Translation/Dumper/PoFileDumper.php b/src/Symfony/Component/Translation/Dumper/PoFileDumper.php
index 5f60086285f9..984281658334 100644
--- a/src/Symfony/Component/Translation/Dumper/PoFileDumper.php
+++ b/src/Symfony/Component/Translation/Dumper/PoFileDumper.php
@@ -23,7 +23,7 @@ class PoFileDumper extends FileDumper
     /**
      * {@inheritdoc}
      */
-    public function formatCatalogue(MessageCatalogue $messages, $domain, array $options = [])
+    public function formatCatalogue(MessageCatalogue $messages, string $domain, array $options = [])
     {
         $output = 'msgid ""'."\n";
         $output .= 'msgstr ""'."\n";
diff --git a/src/Symfony/Component/Translation/Dumper/QtFileDumper.php b/src/Symfony/Component/Translation/Dumper/QtFileDumper.php
index 79a64b2430c5..406e9f0060b7 100644
--- a/src/Symfony/Component/Translation/Dumper/QtFileDumper.php
+++ b/src/Symfony/Component/Translation/Dumper/QtFileDumper.php
@@ -23,7 +23,7 @@ class QtFileDumper extends FileDumper
     /**
      * {@inheritdoc}
      */
-    public function formatCatalogue(MessageCatalogue $messages, $domain, array $options = [])
+    public function formatCatalogue(MessageCatalogue $messages, string $domain, array $options = [])
     {
         $dom = new \DOMDocument('1.0', 'utf-8');
         $dom->formatOutput = true;
diff --git a/src/Symfony/Component/Translation/Dumper/XliffFileDumper.php b/src/Symfony/Component/Translation/Dumper/XliffFileDumper.php
index 8d2694f24e2d..b14713cc34b2 100644
--- a/src/Symfony/Component/Translation/Dumper/XliffFileDumper.php
+++ b/src/Symfony/Component/Translation/Dumper/XliffFileDumper.php
@@ -24,7 +24,7 @@ class XliffFileDumper extends FileDumper
     /**
      * {@inheritdoc}
      */
-    public function formatCatalogue(MessageCatalogue $messages, $domain, array $options = [])
+    public function formatCatalogue(MessageCatalogue $messages, string $domain, array $options = [])
     {
         $xliffVersion = '1.2';
         if (\array_key_exists('xliff_version', $options)) {
diff --git a/src/Symfony/Component/Translation/Dumper/YamlFileDumper.php b/src/Symfony/Component/Translation/Dumper/YamlFileDumper.php
index d6e4af8fb6ff..ac589c975ec5 100644
--- a/src/Symfony/Component/Translation/Dumper/YamlFileDumper.php
+++ b/src/Symfony/Component/Translation/Dumper/YamlFileDumper.php
@@ -33,7 +33,7 @@ public function __construct(string $extension = 'yml')
     /**
      * {@inheritdoc}
      */
-    public function formatCatalogue(MessageCatalogue $messages, $domain, array $options = [])
+    public function formatCatalogue(MessageCatalogue $messages, string $domain, array $options = [])
     {
         if (!class_exists('Symfony\Component\Yaml\Yaml')) {
             throw new LogicException('Dumping translations in the YAML format requires the Symfony Yaml component.');
diff --git a/src/Symfony/Component/Translation/Extractor/AbstractFileExtractor.php b/src/Symfony/Component/Translation/Extractor/AbstractFileExtractor.php
index 8d722dad81df..f532f51c4a1e 100644
--- a/src/Symfony/Component/Translation/Extractor/AbstractFileExtractor.php
+++ b/src/Symfony/Component/Translation/Extractor/AbstractFileExtractor.php
@@ -49,13 +49,11 @@ private function toSplFileInfo(string $file): \SplFileInfo
     }
 
     /**
-     * @param string $file
-     *
      * @return bool
      *
      * @throws InvalidArgumentException
      */
-    protected function isFile($file)
+    protected function isFile(string $file)
     {
         if (!is_file($file)) {
             throw new InvalidArgumentException(sprintf('The "%s" file does not exist.', $file));
@@ -65,11 +63,9 @@ protected function isFile($file)
     }
 
     /**
-     * @param string $file
-     *
      * @return bool
      */
-    abstract protected function canBeExtracted($file);
+    abstract protected function canBeExtracted(string $file);
 
     /**
      * @param string|array $resource Files, a file or a directory
diff --git a/src/Symfony/Component/Translation/Extractor/ChainExtractor.php b/src/Symfony/Component/Translation/Extractor/ChainExtractor.php
index 69ee2dfc39e6..1fe27f1fb3c2 100644
--- a/src/Symfony/Component/Translation/Extractor/ChainExtractor.php
+++ b/src/Symfony/Component/Translation/Extractor/ChainExtractor.php
@@ -33,7 +33,7 @@ class ChainExtractor implements ExtractorInterface
      * @param string             $format    The format of the loader
      * @param ExtractorInterface $extractor The loader
      */
-    public function addExtractor($format, ExtractorInterface $extractor)
+    public function addExtractor(string $format, ExtractorInterface $extractor)
     {
         $this->extractors[$format] = $extractor;
     }
@@ -41,7 +41,7 @@ public function addExtractor($format, ExtractorInterface $extractor)
     /**
      * {@inheritdoc}
      */
-    public function setPrefix($prefix)
+    public function setPrefix(string $prefix)
     {
         foreach ($this->extractors as $extractor) {
             $extractor->setPrefix($prefix);
diff --git a/src/Symfony/Component/Translation/Extractor/ExtractorInterface.php b/src/Symfony/Component/Translation/Extractor/ExtractorInterface.php
index b4534fae7e9e..c26acd22730a 100644
--- a/src/Symfony/Component/Translation/Extractor/ExtractorInterface.php
+++ b/src/Symfony/Component/Translation/Extractor/ExtractorInterface.php
@@ -34,5 +34,5 @@ public function extract($resource, MessageCatalogue $catalogue);
      *
      * @param string $prefix The prefix
      */
-    public function setPrefix($prefix);
+    public function setPrefix(string $prefix);
 }
diff --git a/src/Symfony/Component/Translation/Extractor/PhpExtractor.php b/src/Symfony/Component/Translation/Extractor/PhpExtractor.php
index cd7e02d4c3a1..db9c2bda4e5e 100644
--- a/src/Symfony/Component/Translation/Extractor/PhpExtractor.php
+++ b/src/Symfony/Component/Translation/Extractor/PhpExtractor.php
@@ -72,7 +72,7 @@ public function extract($resource, MessageCatalogue $catalog)
     /**
      * {@inheritdoc}
      */
-    public function setPrefix($prefix)
+    public function setPrefix(string $prefix)
     {
         $this->prefix = $prefix;
     }
diff --git a/src/Symfony/Component/Translation/Extractor/PhpStringTokenParser.php b/src/Symfony/Component/Translation/Extractor/PhpStringTokenParser.php
index 8a8ccb1f1aae..6d7cb96f4337 100644
--- a/src/Symfony/Component/Translation/Extractor/PhpStringTokenParser.php
+++ b/src/Symfony/Component/Translation/Extractor/PhpStringTokenParser.php
@@ -67,7 +67,7 @@ class PhpStringTokenParser
      *
      * @return string The parsed string
      */
-    public static function parse($str)
+    public static function parse(string $str)
     {
         $bLength = 0;
         if ('b' === $str[0]) {
@@ -93,7 +93,7 @@ public static function parse($str)
      *
      * @return string String with escape sequences parsed
      */
-    public static function parseEscapeSequences($str, $quote)
+    public static function parseEscapeSequences(string $str, string $quote = null)
     {
         if (null !== $quote) {
             $str = str_replace('\\'.$quote, $quote, $str);
@@ -127,7 +127,7 @@ private static function parseCallback($matches)
      *
      * @return string Parsed string
      */
-    public static function parseDocString($startToken, $str)
+    public static function parseDocString(string $startToken, string $str)
     {
         // strip last newline (thanks tokenizer for sticking it into the string!)
         $str = preg_replace('~(\r\n|\n|\r)$~', '', $str);
diff --git a/src/Symfony/Component/Translation/Formatter/MessageFormatter.php b/src/Symfony/Component/Translation/Formatter/MessageFormatter.php
index 4bbe0210b609..c5fd2cea6466 100644
--- a/src/Symfony/Component/Translation/Formatter/MessageFormatter.php
+++ b/src/Symfony/Component/Translation/Formatter/MessageFormatter.php
@@ -34,7 +34,7 @@ public function __construct(TranslatorInterface $translator = null, IntlFormatte
     /**
      * {@inheritdoc}
      */
-    public function format($message, $locale, array $parameters = [])
+    public function format(string $message, string $locale, array $parameters = [])
     {
         if ($this->translator instanceof TranslatorInterface) {
             return $this->translator->trans($message, $parameters, null, $locale);
diff --git a/src/Symfony/Component/Translation/Formatter/MessageFormatterInterface.php b/src/Symfony/Component/Translation/Formatter/MessageFormatterInterface.php
index 370c055866c0..b85dbfd115c1 100644
--- a/src/Symfony/Component/Translation/Formatter/MessageFormatterInterface.php
+++ b/src/Symfony/Component/Translation/Formatter/MessageFormatterInterface.php
@@ -26,5 +26,5 @@ interface MessageFormatterInterface
      *
      * @return string
      */
-    public function format($message, $locale, array $parameters = []);
+    public function format(string $message, string $locale, array $parameters = []);
 }
diff --git a/src/Symfony/Component/Translation/Loader/ArrayLoader.php b/src/Symfony/Component/Translation/Loader/ArrayLoader.php
index 2e9a4285ec97..0758da8b59a5 100644
--- a/src/Symfony/Component/Translation/Loader/ArrayLoader.php
+++ b/src/Symfony/Component/Translation/Loader/ArrayLoader.php
@@ -23,7 +23,7 @@ class ArrayLoader implements LoaderInterface
     /**
      * {@inheritdoc}
      */
-    public function load($resource, $locale, $domain = 'messages')
+    public function load($resource, string $locale, string $domain = 'messages')
     {
         $resource = $this->flatten($resource);
         $catalogue = new MessageCatalogue($locale);
diff --git a/src/Symfony/Component/Translation/Loader/CsvFileLoader.php b/src/Symfony/Component/Translation/Loader/CsvFileLoader.php
index 18cc83ed686c..94b928fe93e2 100644
--- a/src/Symfony/Component/Translation/Loader/CsvFileLoader.php
+++ b/src/Symfony/Component/Translation/Loader/CsvFileLoader.php
@@ -51,12 +51,8 @@ protected function loadResource($resource)
 
     /**
      * Sets the delimiter, enclosure, and escape character for CSV.
-     *
-     * @param string $delimiter Delimiter character
-     * @param string $enclosure Enclosure character
-     * @param string $escape    Escape character
      */
-    public function setCsvControl($delimiter = ';', $enclosure = '"', $escape = '\\')
+    public function setCsvControl(string $delimiter = ';', string $enclosure = '"', string $escape = '\\')
     {
         $this->delimiter = $delimiter;
         $this->enclosure = $enclosure;
diff --git a/src/Symfony/Component/Translation/Loader/FileLoader.php b/src/Symfony/Component/Translation/Loader/FileLoader.php
index 7ec54a3c874f..60c5b348e8af 100644
--- a/src/Symfony/Component/Translation/Loader/FileLoader.php
+++ b/src/Symfony/Component/Translation/Loader/FileLoader.php
@@ -23,7 +23,7 @@ abstract class FileLoader extends ArrayLoader
     /**
      * {@inheritdoc}
      */
-    public function load($resource, $locale, $domain = 'messages')
+    public function load($resource, string $locale, string $domain = 'messages')
     {
         if (!stream_is_local($resource)) {
             throw new InvalidResourceException(sprintf('This is not a local file "%s".', $resource));
diff --git a/src/Symfony/Component/Translation/Loader/IcuDatFileLoader.php b/src/Symfony/Component/Translation/Loader/IcuDatFileLoader.php
index 7bbf4c200647..6052ded55d87 100644
--- a/src/Symfony/Component/Translation/Loader/IcuDatFileLoader.php
+++ b/src/Symfony/Component/Translation/Loader/IcuDatFileLoader.php
@@ -26,7 +26,7 @@ class IcuDatFileLoader extends IcuResFileLoader
     /**
      * {@inheritdoc}
      */
-    public function load($resource, $locale, $domain = 'messages')
+    public function load($resource, string $locale, string $domain = 'messages')
     {
         if (!stream_is_local($resource.'.dat')) {
             throw new InvalidResourceException(sprintf('This is not a local file "%s".', $resource));
diff --git a/src/Symfony/Component/Translation/Loader/IcuResFileLoader.php b/src/Symfony/Component/Translation/Loader/IcuResFileLoader.php
index 005f26084d84..dda9284ba4ad 100644
--- a/src/Symfony/Component/Translation/Loader/IcuResFileLoader.php
+++ b/src/Symfony/Component/Translation/Loader/IcuResFileLoader.php
@@ -26,7 +26,7 @@ class IcuResFileLoader implements LoaderInterface
     /**
      * {@inheritdoc}
      */
-    public function load($resource, $locale, $domain = 'messages')
+    public function load($resource, string $locale, string $domain = 'messages')
     {
         if (!stream_is_local($resource)) {
             throw new InvalidResourceException(sprintf('This is not a local file "%s".', $resource));
@@ -75,7 +75,7 @@ public function load($resource, $locale, $domain = 'messages')
      *
      * @return array the flattened ResourceBundle
      */
-    protected function flatten(\ResourceBundle $rb, array &$messages = [], $path = null)
+    protected function flatten(\ResourceBundle $rb, array &$messages = [], string $path = null)
     {
         foreach ($rb as $key => $value) {
             $nodePath = $path ? $path.'.'.$key : $key;
diff --git a/src/Symfony/Component/Translation/Loader/JsonFileLoader.php b/src/Symfony/Component/Translation/Loader/JsonFileLoader.php
index 526721277d76..b31a8d43fb4e 100644
--- a/src/Symfony/Component/Translation/Loader/JsonFileLoader.php
+++ b/src/Symfony/Component/Translation/Loader/JsonFileLoader.php
@@ -44,7 +44,7 @@ protected function loadResource($resource)
      *
      * @return string Message string
      */
-    private function getJSONErrorMessage($errorCode)
+    private function getJSONErrorMessage(int $errorCode)
     {
         switch ($errorCode) {
             case JSON_ERROR_DEPTH:
diff --git a/src/Symfony/Component/Translation/Loader/LoaderInterface.php b/src/Symfony/Component/Translation/Loader/LoaderInterface.php
index 1785402d9cb2..2073f2b24ace 100644
--- a/src/Symfony/Component/Translation/Loader/LoaderInterface.php
+++ b/src/Symfony/Component/Translation/Loader/LoaderInterface.php
@@ -34,5 +34,5 @@ interface LoaderInterface
      * @throws NotFoundResourceException when the resource cannot be found
      * @throws InvalidResourceException  when the resource cannot be loaded
      */
-    public function load($resource, $locale, $domain = 'messages');
+    public function load($resource, string $locale, string $domain = 'messages');
 }
diff --git a/src/Symfony/Component/Translation/Loader/QtFileLoader.php b/src/Symfony/Component/Translation/Loader/QtFileLoader.php
index 2d4a4c084fe4..f5cdec697261 100644
--- a/src/Symfony/Component/Translation/Loader/QtFileLoader.php
+++ b/src/Symfony/Component/Translation/Loader/QtFileLoader.php
@@ -27,7 +27,7 @@ class QtFileLoader implements LoaderInterface
     /**
      * {@inheritdoc}
      */
-    public function load($resource, $locale, $domain = 'messages')
+    public function load($resource, string $locale, string $domain = 'messages')
     {
         if (!stream_is_local($resource)) {
             throw new InvalidResourceException(sprintf('This is not a local file "%s".', $resource));
diff --git a/src/Symfony/Component/Translation/Loader/XliffFileLoader.php b/src/Symfony/Component/Translation/Loader/XliffFileLoader.php
index 6e01a7119ba6..df90978742ad 100644
--- a/src/Symfony/Component/Translation/Loader/XliffFileLoader.php
+++ b/src/Symfony/Component/Translation/Loader/XliffFileLoader.php
@@ -28,7 +28,7 @@ class XliffFileLoader implements LoaderInterface
     /**
      * {@inheritdoc}
      */
-    public function load($resource, $locale, $domain = 'messages')
+    public function load($resource, string $locale, string $domain = 'messages')
     {
         if (!stream_is_local($resource)) {
             throw new InvalidResourceException(sprintf('This is not a local file "%s".', $resource));
@@ -48,7 +48,7 @@ public function load($resource, $locale, $domain = 'messages')
         return $catalogue;
     }
 
-    private function extract($resource, MessageCatalogue $catalogue, $domain)
+    private function extract($resource, MessageCatalogue $catalogue, string $domain)
     {
         try {
             $dom = XmlUtils::loadFile($resource);
diff --git a/src/Symfony/Component/Translation/LoggingTranslator.php b/src/Symfony/Component/Translation/LoggingTranslator.php
index e2414a7d9f22..2c492a16799e 100644
--- a/src/Symfony/Component/Translation/LoggingTranslator.php
+++ b/src/Symfony/Component/Translation/LoggingTranslator.php
@@ -78,7 +78,7 @@ public function getLocale()
     /**
      * {@inheritdoc}
      */
-    public function getCatalogue($locale = null)
+    public function getCatalogue(string $locale = null)
     {
         return $this->translator->getCatalogue($locale);
     }
diff --git a/src/Symfony/Component/Translation/MessageCatalogue.php b/src/Symfony/Component/Translation/MessageCatalogue.php
index 19afb903f7a7..d6b57298cac6 100644
--- a/src/Symfony/Component/Translation/MessageCatalogue.php
+++ b/src/Symfony/Component/Translation/MessageCatalogue.php
@@ -65,7 +65,7 @@ public function getDomains()
     /**
      * {@inheritdoc}
      */
-    public function all($domain = null)
+    public function all(string $domain = null)
     {
         if (null !== $domain) {
             return ($this->messages[$domain.self::INTL_DOMAIN_SUFFIX] ?? []) + ($this->messages[$domain] ?? []);
@@ -89,7 +89,7 @@ public function all($domain = null)
     /**
      * {@inheritdoc}
      */
-    public function set($id, $translation, $domain = 'messages')
+    public function set(string $id, string $translation, string $domain = 'messages')
     {
         $this->add([$id => $translation], $domain);
     }
@@ -97,7 +97,7 @@ public function set($id, $translation, $domain = 'messages')
     /**
      * {@inheritdoc}
      */
-    public function has($id, $domain = 'messages')
+    public function has(string $id, string $domain = 'messages')
     {
         if (isset($this->messages[$domain][$id]) || isset($this->messages[$domain.self::INTL_DOMAIN_SUFFIX][$id])) {
             return true;
@@ -113,7 +113,7 @@ public function has($id, $domain = 'messages')
     /**
      * {@inheritdoc}
      */
-    public function defines($id, $domain = 'messages')
+    public function defines(string $id, string $domain = 'messages')
     {
         return isset($this->messages[$domain][$id]) || isset($this->messages[$domain.self::INTL_DOMAIN_SUFFIX][$id]);
     }
@@ -121,7 +121,7 @@ public function defines($id, $domain = 'messages')
     /**
      * {@inheritdoc}
      */
-    public function get($id, $domain = 'messages')
+    public function get(string $id, string $domain = 'messages')
     {
         if (isset($this->messages[$domain.self::INTL_DOMAIN_SUFFIX][$id])) {
             return $this->messages[$domain.self::INTL_DOMAIN_SUFFIX][$id];
@@ -141,7 +141,7 @@ public function get($id, $domain = 'messages')
     /**
      * {@inheritdoc}
      */
-    public function replace($messages, $domain = 'messages')
+    public function replace(array $messages, string $domain = 'messages')
     {
         unset($this->messages[$domain], $this->messages[$domain.self::INTL_DOMAIN_SUFFIX]);
 
@@ -151,7 +151,7 @@ public function replace($messages, $domain = 'messages')
     /**
      * {@inheritdoc}
      */
-    public function add($messages, $domain = 'messages')
+    public function add(array $messages, string $domain = 'messages')
     {
         if (!isset($this->messages[$domain])) {
             $this->messages[$domain] = $messages;
@@ -246,7 +246,7 @@ public function addResource(ResourceInterface $resource)
     /**
      * {@inheritdoc}
      */
-    public function getMetadata($key = '', $domain = 'messages')
+    public function getMetadata(string $key = '', string $domain = 'messages')
     {
         if ('' == $domain) {
             return $this->metadata;
@@ -266,7 +266,7 @@ public function getMetadata($key = '', $domain = 'messages')
     /**
      * {@inheritdoc}
      */
-    public function setMetadata($key, $value, $domain = 'messages')
+    public function setMetadata(string $key, $value, string $domain = 'messages')
     {
         $this->metadata[$domain][$key] = $value;
     }
@@ -274,7 +274,7 @@ public function setMetadata($key, $value, $domain = 'messages')
     /**
      * {@inheritdoc}
      */
-    public function deleteMetadata($key = '', $domain = 'messages')
+    public function deleteMetadata(string $key = '', string $domain = 'messages')
     {
         if ('' == $domain) {
             $this->metadata = [];
diff --git a/src/Symfony/Component/Translation/MessageCatalogueInterface.php b/src/Symfony/Component/Translation/MessageCatalogueInterface.php
index f3d3f5ea9c9b..6683eeb834b8 100644
--- a/src/Symfony/Component/Translation/MessageCatalogueInterface.php
+++ b/src/Symfony/Component/Translation/MessageCatalogueInterface.php
@@ -45,7 +45,7 @@ public function getDomains();
      *
      * @return array An array of messages
      */
-    public function all($domain = null);
+    public function all(string $domain = null);
 
     /**
      * Sets a message translation.
@@ -54,7 +54,7 @@ public function all($domain = null);
      * @param string $translation The messages translation
      * @param string $domain      The domain name
      */
-    public function set($id, $translation, $domain = 'messages');
+    public function set(string $id, string $translation, string $domain = 'messages');
 
     /**
      * Checks if a message has a translation.
@@ -64,7 +64,7 @@ public function set($id, $translation, $domain = 'messages');
      *
      * @return bool true if the message has a translation, false otherwise
      */
-    public function has($id, $domain = 'messages');
+    public function has(string $id, string $domain = 'messages');
 
     /**
      * Checks if a message has a translation (it does not take into account the fallback mechanism).
@@ -74,7 +74,7 @@ public function has($id, $domain = 'messages');
      *
      * @return bool true if the message has a translation, false otherwise
      */
-    public function defines($id, $domain = 'messages');
+    public function defines(string $id, string $domain = 'messages');
 
     /**
      * Gets a message translation.
@@ -84,7 +84,7 @@ public function defines($id, $domain = 'messages');
      *
      * @return string The message translation
      */
-    public function get($id, $domain = 'messages');
+    public function get(string $id, string $domain = 'messages');
 
     /**
      * Sets translations for a given domain.
@@ -92,7 +92,7 @@ public function get($id, $domain = 'messages');
      * @param array  $messages An array of translations
      * @param string $domain   The domain name
      */
-    public function replace($messages, $domain = 'messages');
+    public function replace(array $messages, string $domain = 'messages');
 
     /**
      * Adds translations for a given domain.
@@ -100,7 +100,7 @@ public function replace($messages, $domain = 'messages');
      * @param array  $messages An array of translations
      * @param string $domain   The domain name
      */
-    public function add($messages, $domain = 'messages');
+    public function add(array $messages, string $domain = 'messages');
 
     /**
      * Merges translations from the given Catalogue into the current one.
diff --git a/src/Symfony/Component/Translation/MetadataAwareInterface.php b/src/Symfony/Component/Translation/MetadataAwareInterface.php
index e93c6fbc7131..d157a072eb84 100644
--- a/src/Symfony/Component/Translation/MetadataAwareInterface.php
+++ b/src/Symfony/Component/Translation/MetadataAwareInterface.php
@@ -30,7 +30,7 @@ interface MetadataAwareInterface
      *
      * @return mixed The value that was set or an array with the domains/keys or null
      */
-    public function getMetadata($key = '', $domain = 'messages');
+    public function getMetadata(string $key = '', string $domain = 'messages');
 
     /**
      * Adds metadata to a message domain.
@@ -39,7 +39,7 @@ public function getMetadata($key = '', $domain = 'messages');
      * @param mixed  $value  The value
      * @param string $domain The domain name
      */
-    public function setMetadata($key, $value, $domain = 'messages');
+    public function setMetadata(string $key, $value, string $domain = 'messages');
 
     /**
      * Deletes metadata for the given key and domain.
@@ -50,5 +50,5 @@ public function setMetadata($key, $value, $domain = 'messages');
      * @param string $key    The key
      * @param string $domain The domain name
      */
-    public function deleteMetadata($key = '', $domain = 'messages');
+    public function deleteMetadata(string $key = '', string $domain = 'messages');
 }
diff --git a/src/Symfony/Component/Translation/Reader/TranslationReader.php b/src/Symfony/Component/Translation/Reader/TranslationReader.php
index e4554f39b4ee..8bb418dcf774 100644
--- a/src/Symfony/Component/Translation/Reader/TranslationReader.php
+++ b/src/Symfony/Component/Translation/Reader/TranslationReader.php
@@ -35,7 +35,7 @@ class TranslationReader implements TranslationReaderInterface
      * @param string          $format The format of the loader
      * @param LoaderInterface $loader
      */
-    public function addLoader($format, LoaderInterface $loader)
+    public function addLoader(string $format, LoaderInterface $loader)
     {
         $this->loaders[$format] = $loader;
     }
@@ -43,7 +43,7 @@ public function addLoader($format, LoaderInterface $loader)
     /**
      * {@inheritdoc}
      */
-    public function read($directory, MessageCatalogue $catalogue)
+    public function read(string $directory, MessageCatalogue $catalogue)
     {
         if (!is_dir($directory)) {
             return;
diff --git a/src/Symfony/Component/Translation/Reader/TranslationReaderInterface.php b/src/Symfony/Component/Translation/Reader/TranslationReaderInterface.php
index 0aa55c6d367d..bc37204f95cb 100644
--- a/src/Symfony/Component/Translation/Reader/TranslationReaderInterface.php
+++ b/src/Symfony/Component/Translation/Reader/TranslationReaderInterface.php
@@ -22,9 +22,6 @@ interface TranslationReaderInterface
 {
     /**
      * Reads translation messages from a directory to the catalogue.
-     *
-     * @param string           $directory
-     * @param MessageCatalogue $catalogue
      */
-    public function read($directory, MessageCatalogue $catalogue);
+    public function read(string $directory, MessageCatalogue $catalogue);
 }
diff --git a/src/Symfony/Component/Translation/Translator.php b/src/Symfony/Component/Translation/Translator.php
index 202d4c259611..006c8991ac42 100644
--- a/src/Symfony/Component/Translation/Translator.php
+++ b/src/Symfony/Component/Translation/Translator.php
@@ -109,7 +109,7 @@ public function setConfigCacheFactory(ConfigCacheFactoryInterface $configCacheFa
      * @param string          $format The name of the loader (@see addResource())
      * @param LoaderInterface $loader A LoaderInterface instance
      */
-    public function addLoader($format, LoaderInterface $loader)
+    public function addLoader(string $format, LoaderInterface $loader)
     {
         $this->loaders[$format] = $loader;
     }
@@ -124,7 +124,7 @@ public function addLoader($format, LoaderInterface $loader)
      *
      * @throws InvalidArgumentException If the locale contains invalid characters
      */
-    public function addResource($format, $resource, $locale, $domain = null)
+    public function addResource(string $format, $resource, string $locale, string $domain = null)
     {
         if (null === $domain) {
             $domain = 'messages';
@@ -220,7 +220,7 @@ public function trans($id, array $parameters = [], $domain = null, $locale = nul
     /**
      * {@inheritdoc}
      */
-    public function getCatalogue($locale = null)
+    public function getCatalogue(string $locale = null)
     {
         if (null === $locale) {
             $locale = $this->getLocale();
@@ -248,7 +248,7 @@ protected function getLoaders()
     /**
      * @param string $locale
      */
-    protected function loadCatalogue($locale)
+    protected function loadCatalogue(string $locale)
     {
         if (null === $this->cacheDir) {
             $this->initializeCatalogue($locale);
@@ -260,7 +260,7 @@ protected function loadCatalogue($locale)
     /**
      * @param string $locale
      */
-    protected function initializeCatalogue($locale)
+    protected function initializeCatalogue(string $locale)
     {
         $this->assertValidLocale($locale);
 
diff --git a/src/Symfony/Component/Translation/TranslatorBagInterface.php b/src/Symfony/Component/Translation/TranslatorBagInterface.php
index 5e49e2ddc545..e40ca8a23bf4 100644
--- a/src/Symfony/Component/Translation/TranslatorBagInterface.php
+++ b/src/Symfony/Component/Translation/TranslatorBagInterface.php
@@ -29,5 +29,5 @@ interface TranslatorBagInterface
      *
      * @throws InvalidArgumentException If the locale contains invalid characters
      */
-    public function getCatalogue($locale = null);
+    public function getCatalogue(string $locale = null);
 }
diff --git a/src/Symfony/Component/Translation/Util/ArrayConverter.php b/src/Symfony/Component/Translation/Util/ArrayConverter.php
index 22c602e7197e..acfbfc363e8b 100644
--- a/src/Symfony/Component/Translation/Util/ArrayConverter.php
+++ b/src/Symfony/Component/Translation/Util/ArrayConverter.php
@@ -84,7 +84,7 @@ private static function &getElementByPath(array &$tree, array $parts)
         return $elem;
     }
 
-    private static function cancelExpand(array &$tree, $prefix, array $node)
+    private static function cancelExpand(array &$tree, string $prefix, array $node)
     {
         $prefix .= '.';
 
diff --git a/src/Symfony/Component/Translation/Writer/TranslationWriter.php b/src/Symfony/Component/Translation/Writer/TranslationWriter.php
index d714d57ea1d9..c8196a4287e2 100644
--- a/src/Symfony/Component/Translation/Writer/TranslationWriter.php
+++ b/src/Symfony/Component/Translation/Writer/TranslationWriter.php
@@ -55,7 +55,7 @@ public function getFormats()
      *
      * @throws InvalidArgumentException
      */
-    public function write(MessageCatalogue $catalogue, $format, $options = [])
+    public function write(MessageCatalogue $catalogue, string $format, array $options = [])
     {
         if (!isset($this->dumpers[$format])) {
             throw new InvalidArgumentException(sprintf('There is no dumper associated with format "%s".', $format));
diff --git a/src/Symfony/Component/Translation/Writer/TranslationWriterInterface.php b/src/Symfony/Component/Translation/Writer/TranslationWriterInterface.php
index b07c08e2366c..52599786d75e 100644
--- a/src/Symfony/Component/Translation/Writer/TranslationWriterInterface.php
+++ b/src/Symfony/Component/Translation/Writer/TranslationWriterInterface.php
@@ -30,5 +30,5 @@ interface TranslationWriterInterface
      *
      * @throws InvalidArgumentException
      */
-    public function write(MessageCatalogue $catalogue, $format, $options = []);
+    public function write(MessageCatalogue $catalogue, string $format, array $options = []);
 }