diff --git a/files/_locales/remove.txt b/files/_locales/remove.txt
new file mode 100644
index 00000000000..977321426cf
--- /dev/null
+++ b/files/_locales/remove.txt
@@ -0,0 +1,3 @@
+Vous pouvez effacer ce fichier sans dommages.
+
+You can safely remove this file.
diff --git a/inc/based_config.php b/inc/based_config.php
index ba7260459de..9075081e19e 100644
--- a/inc/based_config.php
+++ b/inc/based_config.php
@@ -85,6 +85,12 @@
    define("GLPI_SESSION_DIR", GLPI_VAR_DIR . "/_sessions");
 }
 
+// Path for local i18n files
+define('GLPI_I18N_DIR', GLPI_ROOT . "/locales");
+if (!defined("GLPI_LOCAL_I18N_DIR")) {
+   define("GLPI_LOCAL_I18N_DIR", GLPI_VAR_DIR . "/_locales");
+}
+
 // Path for plugins documents storage
 if (!defined("GLPI_PLUGIN_DOC_DIR")) {
    define("GLPI_PLUGIN_DOC_DIR", GLPI_VAR_DIR . "/_plugins");
diff --git a/inc/plugin.class.php b/inc/plugin.class.php
index b8d9713fa67..332d22b50ea 100644
--- a/inc/plugin.class.php
+++ b/inc/plugin.class.php
@@ -197,40 +197,37 @@ static function loadLang($name, $forcelang = '', $coretrytoload = '') {
 
       $dir = GLPI_ROOT . "/plugins/$name/locales/";
 
-      $translation_included = false;
+      $mofile = false;
       // New localisation system
       if (file_exists($dir.$CFG_GLPI["languages"][$trytoload][1])) {
-         $TRANSLATE->addTranslationFile('gettext',
-                                        $dir.$CFG_GLPI["languages"][$trytoload][1],
-                                        $name, $coretrytoload);
-
-         $translation_included = true;
-
+         $mofile = $dir.$CFG_GLPI["languages"][$trytoload][1];
       } else if (!empty($CFG_GLPI["language"])
                  && file_exists($dir.$CFG_GLPI["languages"][$CFG_GLPI["language"]][1])) {
-         $TRANSLATE->addTranslationFile('gettext',
-                                        $dir.$CFG_GLPI["languages"][$CFG_GLPI["language"]][1],
-                                        $name, $coretrytoload);
-         $translation_included = true;
+         $mofile = $dir.$CFG_GLPI["languages"][$CFG_GLPI["language"]][1];
       } else if (file_exists($dir."en_GB.mo")) {
-         $TRANSLATE->addTranslationFile('gettext',
-                                        $dir."en_GB.mo",
-                                        $name, $coretrytoload);
-         $translation_included = true;
-
-      }
-
-      if (!$translation_included) {
-         if (file_exists($dir.$trytoload.'.php')) {
-            include ($dir.$trytoload.'.php');
-         } else if (isset($CFG_GLPI["language"])
-                    && file_exists($dir.$CFG_GLPI["language"].'.php')) {
-            include ($dir.$CFG_GLPI["language"].'.php');
-         } else if (file_exists($dir . "en_GB.php")) {
-            include ($dir . "en_GB.php");
-         } else if (file_exists($dir . "fr_FR.php")) {
-            include ($dir . "fr_FR.php");
-         }
+         $mofile = $dir."en_GB.mo";
+      }
+
+      if ($mofile !== false) {
+         $TRANSLATE->addTranslationFile(
+            'gettext',
+            $mofile,
+            $name,
+            $coretrytoload
+         );
+      }
+
+      $mofile = str_replace($dir, GLPI_LOCAL_I18N_DIR . '/'.$name, $mofile);
+      $phpfile = str_replace('.mo', '.php', $mofile);
+
+      // Load local PHP file if it exists
+      if (file_exists($phpfile)) {
+         $TRANSLATE->addTranslationFile('phparray', $phpfile, $name, $coretrytoload);
+      }
+
+      // Load local MO file if it exists -- keep last so it gets precedence
+      if (file_exists($mofile)) {
+         $TRANSLATE->addTranslationFile('gettext', $mofile, $name, $coretrytoload);
       }
    }
 
diff --git a/inc/session.class.php b/inc/session.class.php
index af17569be22..a876b2f15ab 100644
--- a/inc/session.class.php
+++ b/inc/session.class.php
@@ -593,11 +593,11 @@ static function loadLanguage($forcelang = '', $with_plugins = true) {
       }
 
       if (isset($CFG_GLPI["languages"][$trytoload])) {
-         $newfile = "/locales/" . $CFG_GLPI["languages"][$trytoload][1];
+         $newfile = "/" . $CFG_GLPI["languages"][$trytoload][1];
       }
 
-      if (empty($newfile) || !is_file(GLPI_ROOT . $newfile)) {
-         $newfile = "/locales/en_GB.mo";
+      if (empty($newfile) || !is_file(GLPI_I18N_DIR . $newfile)) {
+         $newfile = "/en_GB.mo";
       }
 
       if (isset($CFG_GLPI["languages"][$trytoload][5])) {
@@ -607,11 +607,24 @@ static function loadLanguage($forcelang = '', $with_plugins = true) {
       $TRANSLATE->setLocale($trytoload);
 
       $cache = Config::getCache('cache_trans', 'core', false);
-      if ($cache !== false) {
+      if ($cache !== false && !defined('TU_USER')) {
          $TRANSLATE->setCache($cache);
       }
 
-      $TRANSLATE->addTranslationFile('gettext', GLPI_ROOT.$newfile, 'glpi', $trytoload);
+      $TRANSLATE->addTranslationFile('gettext', GLPI_I18N_DIR.$newfile, 'glpi', $trytoload);
+
+      $mofile = GLPI_LOCAL_I18N_DIR . '/core/' . $newfile;
+      $phpfile = str_replace('.mo', '.php', $mofile);
+
+      // Load local PHP file if it exists
+      if (file_exists($phpfile)) {
+         $TRANSLATE->addTranslationFile('phparray', $phpfile, 'glpi', $trytoload);
+      }
+
+      // Load local MO file if it exists -- keep last so it gets precedence
+      if (file_exists($mofile)) {
+         $TRANSLATE->addTranslationFile('gettext', $mofile, 'glpi', $trytoload);
+      }
 
       // Load plugin dicts
       if ($with_plugins) {
diff --git a/tests/functionnal/Session.php b/tests/functionnal/Session.php
index 6d44cfe15e8..9d1487212ca 100644
--- a/tests/functionnal/Session.php
+++ b/tests/functionnal/Session.php
@@ -133,4 +133,39 @@ function () {
 
       $this->array($_SESSION['MESSAGE_AFTER_REDIRECT'])->isEmpty();
    }
+
+   public function testLocalI18n() {
+      //load locales
+      \Session::loadLanguage('en_GB');
+      $this->string(__('Login'))->isIdenticalTo('Login');
+
+      //create directory for local i18n
+      if (!file_exists(GLPI_LOCAL_I18N_DIR.'/core')) {
+         mkdir(GLPI_LOCAL_I18N_DIR.'/core');
+      }
+
+      //write local MO file with i18n override
+      copy(
+         __DIR__ . '/../local_en_GB.mo',
+         GLPI_LOCAL_I18N_DIR.'/core/en_GB.mo'
+      );
+      \Session::loadLanguage('en_GB');
+
+      $this->string(__('Login'))->isIdenticalTo('Login from local gettext');
+      $this->string(__('Password'))->isIdenticalTo('Password');
+
+      //write local PHP file with i18n override
+      file_put_contents(
+         GLPI_LOCAL_I18N_DIR.'/core/en_GB.php',
+         "<?php\n\$lang['Login'] = 'Login from local PHP';\n\$lang['Password'] = 'Password from local PHP';\nreturn \$lang;"
+      );
+      \Session::loadLanguage('en_GB');
+
+      $this->string(__('Login'))->isIdenticalTo('Login from local gettext');
+      $this->string(__('Password'))->isIdenticalTo('Password from local PHP');
+
+      //cleanup -- keep at the end
+      unlink(GLPI_LOCAL_I18N_DIR.'/core/en_GB.php');
+      unlink(GLPI_LOCAL_I18N_DIR.'/core/en_GB.mo');
+   }
 }
diff --git a/tests/local_en_GB.mo b/tests/local_en_GB.mo
new file mode 100644
index 00000000000..933878e407a
Binary files /dev/null and b/tests/local_en_GB.mo differ
diff --git a/tests/local_en_GB.po b/tests/local_en_GB.po
new file mode 100644
index 00000000000..94cf79750c8
--- /dev/null
+++ b/tests/local_en_GB.po
@@ -0,0 +1,24 @@
+# Override PO file
+#
+msgid ""
+msgstr ""
+"Project-Id-Version: PACKAGE VERSION\n"
+"Report-Msgid-Bugs-To: \n"
+"POT-Creation-Date: 2019-04-13 10:43+0200\n"
+"PO-Revision-Date: 2019-04-13 10:43+0200\n"
+"Last-Translator: Automatically generated\n"
+"Language-Team: none\n"
+"Language: en_GB\n"
+"MIME-Version: 1.0\n"
+"Content-Type: text/plain; charset=UTF-8\n"
+"Content-Transfer-Encoding: 8bit\n"
+"Plural-Forms: nplurals=2; plural=(n != 1);\n"
+
+#: index.php:131 inc/authldap.class.php:3198 inc/authmail.class.php:231
+#: inc/config.class.php:1762 inc/dbutils.class.php:1647
+#: inc/mailcollector.class.php:270 inc/mailcollector.class.php:473
+#: inc/notificationtargetuser.class.php:107 inc/ruleright.class.php:259
+#: inc/user.class.php:1995 inc/user.class.php:2426 inc/user.class.php:2884
+#: inc/user.class.php:3892
+msgid "Login"
+msgstr "Login from local gettext"