diff --git a/htdocs/core/class/html.formadmin.class.php b/htdocs/core/class/html.formadmin.class.php
index 166e0ce2044..adf3c1cad03 100644
--- a/htdocs/core/class/html.formadmin.class.php
+++ b/htdocs/core/class/html.formadmin.class.php
@@ -57,9 +57,10 @@ class FormAdmin
 	 *  @param		string		$morecss		Add more css styles
 	 *  @param      int         $showcode       1=Add language code into label at begining, 2=Add language code into label at end
      *  @param		int			$forcecombo		Force to use combo box (so no ajax beautify effect)
+     *  @param		int			$multiselect	Make the combo a multiselect
      *  @return		string						Return HTML select string with list of languages
      */
-    public function select_language($selected = '', $htmlname = 'lang_id', $showauto = 0, $filter = null, $showempty = '', $showwarning = 0, $disabled = 0, $morecss = '', $showcode = 0, $forcecombo = 0)
+    public function select_language($selected = '', $htmlname = 'lang_id', $showauto = 0, $filter = null, $showempty = '', $showwarning = 0, $disabled = 0, $morecss = '', $showcode = 0, $forcecombo = 0, $multiselect = 0)
 	{
 		// phpcs:enable
 		global $conf, $langs;
@@ -70,8 +71,8 @@ class FormAdmin
 
 		$out='';
 
-		$out.= '<select class="flat'.($morecss?' '.$morecss:'').'" id="'.$htmlname.'" name="'.$htmlname.'"'.($disabled?' disabled':'').'>';
-		if ($showempty)
+		$out.= '<select '.($multiselect ? 'multiple="multiple" ' : '').'class="flat'.($morecss?' '.$morecss:'').'" id="'.$htmlname.'" name="'.$htmlname.($multiselect?'[]':'').'"'.($disabled?' disabled':'').'>';
+		if ($showempty && ! $multiselect)
 		{
 			$out.= '<option value="0"';
 			if ($selected == '') $out.= ' selected';
diff --git a/htdocs/core/lib/functions.lib.php b/htdocs/core/lib/functions.lib.php
index 6ee6007088b..f95ca35b8a3 100644
--- a/htdocs/core/lib/functions.lib.php
+++ b/htdocs/core/lib/functions.lib.php
@@ -7557,12 +7557,13 @@ function natural_search($fields, $value, $mode = 0, $nofirstand = 0)
 					$i2++;	// a criteria was added to string
 				}
 			}
-			elseif ($mode == 2)
+			elseif ($mode == 2 || $mode == -2)
 			{
-				$newres .= ($i2 > 0 ? ' OR ' : '') . $field . " IN (" . $db->escape(trim($crit)) . ")";
+				$newres .= ($i2 > 0 ? ' OR ' : '') . $field . " ".($mode == -2 ? 'NOT ' : '')."IN (" . $db->escape(trim($crit)) . ")";
+				if ($mode == -2) $newres .= ' OR '.$field.' IS NULL';
 				$i2++;	// a criteria was added to string
 			}
-			elseif ($mode == 3)
+			elseif ($mode == 3 || $mode == -3)
 			{
 				$tmparray=explode(',', trim($crit));
 				if (count($tmparray))
@@ -7576,9 +7577,10 @@ function natural_search($fields, $value, $mode = 0, $nofirstand = 0)
 							$listofcodes.="'".$db->escape(trim($val))."'";
 						}
 					}
-					$newres .= ($i2 > 0 ? ' OR ' : '') . $field . " IN (" . $listofcodes . ")";
+					$newres .= ($i2 > 0 ? ' OR ' : '') . $field . " ".($mode == -3 ? 'NOT ' : '')."IN (" . $listofcodes . ")";
 					$i2++;	// a criteria was added to string
 				}
+				if ($mode == -3) $newres .= ' OR '.$field.' IS NULL';
 			}
 			elseif ($mode == 4)
 			{