add localized tooltip value

config/locales/js-de.yml

@@ -299,6 +299,7 @@ de:
       description_options_show: "Optionen einblenden"
       label_enable_multi_select: "Mehrfachauswahl aktivieren"
       label_disable_multi_select: "Mehrfachauswahl deaktivieren"
+      label_column_multiselect: "Combined dropdown field: Select with arrow keys, confirm selection with enter, delete with backspace"
       label_filter_add: "Filter hinzufügen"
       label_options: "Optionen"
       message_error_during_bulk_delete: Fehler beim Löschen der Arbeitspakete.

config/locales/js-en.yml

@@ -304,6 +304,7 @@ en:
       label_disable_multi_select: "Disable multiselect"
       label_filter_add: "Add filter"
       label_options: "Options"
+      label_column_multiselect: "Combined dropdown field: Select with arrow keys, confirm selection with enter, delete with backspace"
       message_error_during_bulk_delete: An error occurred while trying to delete work packages.
       message_successful_bulk_delete: Successfully deleted work packages.
       no_results:

frontend/app/templates/work_packages/modals/columns.html

@@ -14,6 +14,8 @@
           <div ng-bind-html="column.title | highlight: $select.search"></div>
         </ui-select-choices>
       </ui-select>
+      <i class="icon icon-help1" data-tooltip="{{ I18n.t('js.work_packages.label_column_multiselect') }}"></i>
+
     </div>
 
     <div>