Login as admin Navigate to Site Administration -> Language -> Language customisation Select a language pack and open the language pack for editing Choose the moodle.php file and click show strings Verify that you see a set of "Apply changes and continue editing" and "Save changes to the language pack" buttons before and also after the strings table Change a language string Save the changes to the language pack by clicking on the "Save changes to the language pack" that is shown after the strings table Open the language pack for editing again Verify  you see the changed language string Verify  the background colour for the changed language string row has changed.