diff --git a/engine/classes/Elgg/I18n/ArrayMessageBundle.php b/engine/classes/Elgg/I18n/ArrayMessageBundle.php
new file mode 100644
index 00000000000..56d09dec885
--- /dev/null
+++ b/engine/classes/Elgg/I18n/ArrayMessageBundle.php
@@ -0,0 +1,45 @@
+<?php
+namespace Elgg\I18n;
+
+/**
+ * WARNING: API IN FLUX. DO NOT USE DIRECTLY.
+ * 
+ * Uses an array as a source for the message bundle.
+ * 
+ * This is mostly useful for testing so we can configure translators
+ * in-memory instead of going to the file system.
+ * 
+ * @since 1.11
+ * 
+ * @access private
+ */
+final class ArrayMessageBundle implements MessageBundle {
+	
+	/** @var array */
+	private $messages;
+	
+	/**
+	 * Constructor
+	 * 
+	 * @param array $messages Map of locales to maps of keys to message-templates
+	 */
+	public function __construct(array $messages) {
+		$this->messages = $messages;
+	}
+	
+	/** @inheritDoc */
+	public function get($key, Locale $locale) {
+		assert(is_string($key), '$key must be a string');
+		
+		if (!isset($this->messages["$locale"]) || !is_array($this->messages["$locale"])) {
+			return null;
+		}
+		
+		$messages = $this->messages["$locale"];
+		if (!is_string($key) || !isset($messages[$key]) || !is_string($messages[$key])) {
+			return null;
+		}
+		
+		return new SprintfMessageTemplate($messages[$key]);
+	}
+}
diff --git a/engine/classes/Elgg/I18n/Locale.php b/engine/classes/Elgg/I18n/Locale.php
new file mode 100644
index 00000000000..ff31813f1db
--- /dev/null
+++ b/engine/classes/Elgg/I18n/Locale.php
@@ -0,0 +1,49 @@
+<?php
+namespace Elgg\I18n;
+
+/**
+ * WARNING: API IN FLUX. DO NOT USE DIRECTLY.
+ * 
+ * Language class to ensure only valid languages are used.
+ * 
+ * @since 1.11
+ * 
+ * @access private
+ */
+final class Locale {
+	
+	/** @var string */
+	private $locale;
+	
+	/**
+	 * Use Locale::parse to construct
+	 * 
+	 * @param string $locale A string representation of the locale
+	 */
+	private function __construct($locale) {
+		$this->locale = $locale;
+	}
+	
+	/** @inheritDoc */
+	public function __toString() {
+		return $this->locale;
+	}
+	
+	/**
+	 * Create a language, asserting that the language code is valid.
+	 *
+	 * @param string $locale Language code
+	 * 
+	 * @return Locale
+	 * 
+	 * @throws InvalidLocaleException
+	 */
+	public static function parse($locale) {
+		// TODO(evan): Better sanitizing of locales using \Locale perhaps
+		if (strlen($locale) < 2 || strlen($locale) > 5) {
+			throw new InvalidLocaleException("Unrecognized locale: $locale");
+		}
+		
+		return new Locale($locale);
+	}
+}
\ No newline at end of file
diff --git a/engine/classes/Elgg/I18n/MessageBundle.php b/engine/classes/Elgg/I18n/MessageBundle.php
new file mode 100644
index 00000000000..1d8cd07273f
--- /dev/null
+++ b/engine/classes/Elgg/I18n/MessageBundle.php
@@ -0,0 +1,25 @@
+<?php
+namespace Elgg\I18n;
+
+/**
+ * WARNING: API IN FLUX. DO NOT USE DIRECTLY.
+ * 
+ * TODO(ewinslow): Have this extend Table(row=string, column=Locale, value=?MessageTemplate)
+ *                 if we ever support a Table data structure.
+ * 
+ * @since 1.11
+ * 
+ * @access private
+ */
+interface MessageBundle {
+	
+	/**
+	 * Fetches the translatable message associated with the given key
+	 * 
+	 * @param string $key    String identifier for the message
+	 * @param Locale $locale Locale in which the message is written
+	 * 
+	 * @return ?MessageTemplate The message object or null if not found.
+	 */
+	public function get($key, Locale $locale);
+}
\ No newline at end of file
diff --git a/engine/classes/Elgg/I18n/MessageTemplate.php b/engine/classes/Elgg/I18n/MessageTemplate.php
new file mode 100644
index 00000000000..152e1377ede
--- /dev/null
+++ b/engine/classes/Elgg/I18n/MessageTemplate.php
@@ -0,0 +1,50 @@
+<?php
+namespace Elgg\I18n;
+
+/**
+ * WARNING: API IN FLUX. DO NOT USE DIRECTLY.
+ * 
+ * A single localizable message template.
+ * 
+ * We introduced this class because we want to have the flexibility of
+ * easily switching our message template language from sprintf to ICU...
+ * 
+ * Example messages:
+ *  - "{subject} spent {num_nights,number,integer} nights camping in {location}." (ICU)
+ *  - "%s spent %d nights camping in %s" (sprintf)
+ * 
+ * @since 1.11
+ * 
+ * @access private
+ */
+abstract class MessageTemplate {
+	/** @var string */
+	protected $template;
+	
+	/**
+	 * Constructor
+	 * 
+	 * @param string $template The message template
+	 */
+	public function __construct($template) {
+		$this->template = $template;
+	}
+	
+	/**
+	 * Applies the inputs to the message template and returns the result.
+	 * 
+	 * @param array $args The inputs to this message
+	 * 
+	 * @return string The rendered including all the interpolated inputs
+	 */
+	public abstract function format(array $args);
+	
+	/**
+	 * Get the string template this message uses for translation.
+	 * 
+	 * @return string
+	 */
+	public function __toString() {
+		return $this->template;
+	}
+}
\ No newline at end of file
diff --git a/engine/classes/Elgg/I18n/MessageTranslator.php b/engine/classes/Elgg/I18n/MessageTranslator.php
new file mode 100644
index 00000000000..9357798dccf
--- /dev/null
+++ b/engine/classes/Elgg/I18n/MessageTranslator.php
@@ -0,0 +1,53 @@
+<?php
+namespace Elgg\I18n;
+
+/**
+ * WARNING: API IN FLUX. DO NOT USE DIRECTLY.
+ *
+ * @access private
+ *
+ * @since 1.11
+ */
+class MessageTranslator implements TranslatorInterface {
+	
+	// TODO Maybe this should be an array of locales to provide multiple fallbacks?
+	/** @var Locale */
+	private $defaultLocale;
+	
+	/** @var MessageBundle */
+	private $messages;
+	
+	/**
+	 * Constructor
+	 * 
+	 * @param Locale        $defaultLocale The fallback locale
+	 * @param MessageBundle $messages      Messages that this translator is aware of
+	 */
+	public function __construct(Locale $defaultLocale, MessageBundle $messages) {
+		$this->defaultLocale = $defaultLocale;
+		$this->messages = $messages;
+	}
+	
+	/** @inheritDoc */
+	public function translate($key, array $args = [], Locale $locale = null) {
+		$locales = [
+			$locale,
+			$this->defaultLocale,
+			Locale::parse('en'),
+		];
+		
+		foreach ($locales as $locale) {
+			if (!$locale) {
+				continue;
+			}
+			
+			$message = $this->messages->get($key, $locale);
+			
+			if ($message) {
+				return $message->format($args);
+			}
+		}
+		
+		return $key;
+	}
+}
\ No newline at end of file
diff --git a/engine/classes/Elgg/I18n/NullMessageTemplate.php b/engine/classes/Elgg/I18n/NullMessageTemplate.php
new file mode 100644
index 00000000000..e2d4c1cc34e
--- /dev/null
+++ b/engine/classes/Elgg/I18n/NullMessageTemplate.php
@@ -0,0 +1,18 @@
+<?php
+namespace Elgg\I18n;
+
+/**
+ * WARNING: API IN FLUX. DO NOT USE DIRECTLY.
+ * 
+ * A message that always ignores all parameters and just returns the template.
+ * 
+ * @since 1.11
+ * 
+ * @access private
+ */
+final class NullMessage extends Message {
+	/** @inheritDoc */
+	public function format(array $args) {
+		return "$this";
+	}
+}
\ No newline at end of file
diff --git a/engine/classes/Elgg/I18n/NullTranslator.php b/engine/classes/Elgg/I18n/NullTranslator.php
index 028a1e5e9e2..d4f7b1d7f7c 100644
--- a/engine/classes/Elgg/I18n/NullTranslator.php
+++ b/engine/classes/Elgg/I18n/NullTranslator.php
@@ -5,13 +5,16 @@
 /**
  * WARNING: API IN FLUX. DO NOT USE DIRECTLY.
  *
- * @access private
+ * A translator that does nothing except return the key that was requested.
+ * 
+ * This translator is useful during development if you want to be able to
+ * easily tell what the available keys are for changing the wording of UI elements.
+ * 
+ * @since 1.10.0
  *
- * @package    Elgg.Core
- * @subpackage I18n
- * @since      1.10.0
+ * @access private
  */
-class NullTranslator extends Translator {
+final class NullTranslator extends Translator {
 	/** @inheritDoc */
 	public function translate($key, $args = array(), $lang = '') {
 		return $key;
diff --git a/engine/classes/Elgg/I18n/SprintfMessageTemplate.php b/engine/classes/Elgg/I18n/SprintfMessageTemplate.php
new file mode 100644
index 00000000000..7c77d3b21d0
--- /dev/null
+++ b/engine/classes/Elgg/I18n/SprintfMessageTemplate.php
@@ -0,0 +1,18 @@
+<?php
+namespace Elgg\I18n;
+
+/**
+ * WARNING: API IN FLUX. DO NOT USE DIRECTLY.
+ * 
+ * A message that uses vsprintf to insert arguments into the template.
+ * 
+ * @since 1.11
+ * 
+ * @access private
+ */
+final class SprintfMessageTemplate extends MessageTemplate {
+	/** @inheritDoc */
+	public function format(array $args) {
+		return \vsprintf($this->template, $args);
+	}
+}
\ No newline at end of file
diff --git a/engine/classes/Elgg/I18n/Translator.php b/engine/classes/Elgg/I18n/Translator.php
index be190804d55..4c1aa88b9b6 100644
--- a/engine/classes/Elgg/I18n/Translator.php
+++ b/engine/classes/Elgg/I18n/Translator.php
@@ -6,9 +6,7 @@
  *
  * @access private
  *
- * @package    Elgg.Core
- * @subpackage I18n
- * @since      1.10.0
+ * @since 1.10.0
  */
 class Translator {
 	
diff --git a/engine/classes/Elgg/I18n/TranslatorInterface.php b/engine/classes/Elgg/I18n/TranslatorInterface.php
new file mode 100644
index 00000000000..d468f5a5d31
--- /dev/null
+++ b/engine/classes/Elgg/I18n/TranslatorInterface.php
@@ -0,0 +1,37 @@
+<?php
+namespace Elgg\I18n;
+
+/**
+ * WARNING: API IN FLUX. DO NOT USE DIRECTLY.
+ * 
+ * Can "translate" language keys into various human-readable, localized strings.
+ * 
+ * TODO(ewinslow): Remove the "Interface" suffix
+ * 
+ * @since 1.11
+ * 
+ * @access private
+ */
+interface TranslatorInterface {
+	/**
+	 * Given a message key, returns a best-effort translated string.
+	 * 
+	 * If the translator doesn't know how to translate into the specified locale,
+	 * it can try translating into a related or similar locale (e.g. en-US => en).
+	 * 
+	 * If no locale is specified, or if no translation can be found for the specified
+	 * locale, the translator may choose to fall back to some other language(s).
+	 * 
+	 * It should never throw exceptions, since lack of translation should never be
+	 * cause to bring down an app or cancel a request. However, implementations may
+	 * log warnings to alert admins that requested language strings are missing.
+	 *
+	 * @param string $key    A key identifying the message to translate.
+	 * @param array  $args   An array of arguments with which to format the message.
+	 * @param Locale $locale Optionally, the standard language code
+	 *                       (defaults to site/user default, then English)
+	 *
+	 * @return string The final, best-effort translation.
+	 */
+	function translate($key, array $args = [], Locale $locale = null);
+}
\ No newline at end of file
diff --git a/engine/tests/phpunit/Elgg/I18n/MessageTranslatorTest.php b/engine/tests/phpunit/Elgg/I18n/MessageTranslatorTest.php
new file mode 100644
index 00000000000..d74340b4d18
--- /dev/null
+++ b/engine/tests/phpunit/Elgg/I18n/MessageTranslatorTest.php
@@ -0,0 +1,47 @@
+<?php
+namespace Elgg\I18n;
+
+use PHPUnit_Framework_TestCase as TestCase;
+
+class MessageTranslatorTest extends TestCase {
+	public function setUp() {
+		$this->english = Locale::parse('en');
+		$this->spanish = Locale::parse('es');
+	}
+	
+	public function testKeyIsReturnedIfNoTranslationCanBeFound() {
+		$messages = new ArrayMessageBundle([]);
+		$translator = new MessageTranslator(Locale::parse('en'), $messages);
+		
+		$this->assertEquals('foobar', $translator->translate('foobar'));
+	}
+	
+	public function testTranslateReturnsTranslationForSpecifiedLocaleIfAvailable() {
+		$messages = new ArrayMessageBundle([
+			'en' => ['one' => 'one'],
+			'es' => ['one' => 'uno'],
+		]);
+		$translator = new MessageTranslator(Locale::parse('en'), $messages);
+		
+		$this->assertEquals('uno', $translator->translate('one', [], Locale::parse('es')));
+	}
+	
+	public function testTranslateReturnsTranslationForDefaultLocaleIfNoLocaleWasSpecified() {
+		$messages = new ArrayMessageBundle([
+			'en' => ['one' => 'one'],
+			'es' => ['one' => 'uno'],
+		]);
+		$translator = new MessageTranslator(Locale::parse('en'), $messages);
+		
+		$this->assertEquals('one', $translator->translate('one', []));
+	}
+	
+	public function testFallsBackToLanguageIfTranslationForSpecifiedLanguageIsNotAvailable() {
+		$messages = new ArrayMessageBundle([
+			'en' => ['one' => 'one'],
+		]);
+		$translator = new MessageTranslator(Locale::parse('en'), $messages);
+		
+		$this->assertEquals('one', $translator->translate('one', [], Locale::parse('es')));
+	}
+}
\ No newline at end of file
diff --git a/engine/tests/phpunit/Elgg/I18n/TranslatorTest.php b/engine/tests/phpunit/Elgg/I18n/TranslatorTest.php
index 92aaacf26ea..bb9347b50c5 100644
--- a/engine/tests/phpunit/Elgg/I18n/TranslatorTest.php
+++ b/engine/tests/phpunit/Elgg/I18n/TranslatorTest.php
@@ -12,7 +12,7 @@ public function testSetLanguageFromGetParameter() {
 		_elgg_services()->input->set('hl', $input_lang);
 		
 		$lang = $translator->getLanguage();
-		$this->assertEquals($lang, $input_lang);		
+		$this->assertEquals($lang, $input_lang);
 	}
 	
 	public function testCheckLanguageKeyExists() {
@@ -24,4 +24,7 @@ public function testCheckLanguageKeyExists() {
 		$this->assertFalse($translator->languageKeyExists('__elgg_php_unit:test_key:missing'));
 	}
 	
+	public function testDoesNotPerformSprintfFormattingIfArgsNotProvided() {
+		$this->markTestIncomplete();
+	}
 }
\ No newline at end of file