diff --git a/ChangeLog b/ChangeLog
index 1a1f5fe677a..341858d59ee 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -9,8 +9,10 @@ For users:
 - New: Ask password when creating a user from a contact
 
 For developers:
-- New: External modules can add their menu manager
+- New: External modules can add their own menu manager
 - New: External modules can remove tabs
+- New: A module can overwrite all default language files by forcing
+       priority on langs directories on its own lang directory.
 
 
 ***** ChangeLog for 3.0 compared to 2.9 *****
diff --git a/htdocs/core/class/translate.class.php b/htdocs/core/class/translate.class.php
index 49cdf7fb20f..0704f47dee3 100644
--- a/htdocs/core/class/translate.class.php
+++ b/htdocs/core/class/translate.class.php
@@ -49,30 +49,42 @@ class Translate {
 
 
 	/**
-	 *  \brief      Constructeur de la classe
-	 *  \param      dir             Force directory that contains /langs subdirectory
-	 *  \param      conf			Objet qui contient la config Dolibarr
+	 *  Constructor
+	 *  @param      dir             Force directory that contains /langs subdirectory (value is sometine '..' like into install/* pages
+	 *                              or support/* pages).
+	 *  @param      conf			Object with Dolibarr configuration
 	 */
 	function Translate($dir = "",$conf)
 	{
-		// If charset output is forced
-		if (! empty($conf->file->character_set_client))
-		{
-			$this->charset_output=$conf->file->character_set_client;
-		}
+		if (! empty($conf->file->character_set_client)) $this->charset_output=$conf->file->character_set_client;	// If charset output is forced
 		if ($dir) $this->dir=array($dir);
 		else $this->dir=$conf->file->dol_document_root;
 	}
 
 
+
 	/**
-	 *  \brief      Set accessor for this->defaultlang
-	 *  \param      srclang     	Language to use
+	 *  Set accessor for this->defaultlang
+	 *  @param      srclang     	Language to use
 	 */
 	function setDefaultLang($srclang='fr_FR')
 	{
+		global $conf;
+		
 		//dol_syslog("Translate::setDefaultLang srclang=".$srclang,LOG_DEBUG);
 
+		// If a module ask to force a priority on langs directories (to use its own lang files)
+		if (! empty($conf->global->MAIN_FORCELANGDIR)) 
+		{
+			$more=array();
+			foreach($conf->file->dol_document_root as $dir)
+			{
+				$newdir=$dir.$conf->global->MAIN_FORCELANGDIR;
+				if (! in_array($newdir,$this->dir)) $more[]=$newdir;
+			}
+			$this->dir=array_merge($more,$this->dir);			
+		}
+		
 		$this->origlang=$srclang;
 
 		if (empty($srclang) || $srclang == 'auto')