diff --git a/htdocs/main.inc.php b/htdocs/main.inc.php
index 2647cba166c..99cfe360f9f 100644
--- a/htdocs/main.inc.php
+++ b/htdocs/main.inc.php
@@ -1689,7 +1689,7 @@ function top_htmlhead($head, $title = '', $disablejs = 0, $disablehead = 0, $arr
 
 			// Global js function
 			print '<!-- Includes JS of Dolibarr -->'."\n";
-			print '<script src="'.DOL_URL_ROOT.'/core/js/lib_head.js.php?lang='.$langs->defaultlang.($ext ? '&'.$ext : '').'"></script>'."\n";
+			print '<script src="'.DOL_URL_ROOT.'/core/js/lib_head.js.php?lang='.$langs->defaultlang.($ext ? '&amp;'.$ext : '').'"></script>'."\n";
 
 			// JS forced by modules (relative url starting with /)
 			if (!empty($conf->modules_parts['js'])) {		// $conf->modules_parts['js'] is array('module'=>array('file1','file2'))
@@ -1698,7 +1698,7 @@ function top_htmlhead($head, $title = '', $disablejs = 0, $disablehead = 0, $arr
 					$filesjs = (array) $filesjs; // To be sure filejs is an array
 					foreach ($filesjs as $jsfile) {
 						// jsfile is a relative path
-						print '<!-- Include JS added by module '.$modjs.'-->'."\n".'<script src="'.dol_buildpath($jsfile, 1).'"></script>'."\n";
+						print '<!-- Include JS added by module '.$modjs.'-->'."\n".'<script src="'.dol_buildpath($jsfile, 1).((strpos($jsfile, '?') === false) ? '?' : '&amp;').'lang='.$langs->defaultlang.'"></script>'."\n";
 					}
 				}
 			}
@@ -1707,9 +1707,9 @@ function top_htmlhead($head, $title = '', $disablejs = 0, $disablehead = 0, $arr
 				print '<!-- Includes JS added by page -->'."\n";
 				foreach ($arrayofjs as $jsfile) {
 					if (preg_match('/^(http|\/\/)/i', $jsfile)) {
-						print '<script src="'.$jsfile.($ext ? ((strpos($jsfile, '?') === false) ? '?' : '&').$ext : '').'"></script>'."\n";
+						print '<script src="'.$jsfile.((strpos($jsfile, '?') === false) ? '?' : '&amp;').'lang='.$langs->defaultlang.'"></script>'."\n";
 					} else {
-						print '<script src="'.dol_buildpath($jsfile, 1).($ext ? ((strpos($jsfile, '?') === false) ? '?' : '&').$ext : '').'"></script>'."\n";
+						print '<script src="'.dol_buildpath($jsfile, 1).((strpos($jsfile, '?') === false) ? '?' : '&amp;').'lang='.$langs->defaultlang.'"></script>'."\n";
 					}
 				}
 			}