Verify before start Ensure that, in your config.php, you don't have any line like this: $CFG->langstringcache = false; (comment out the whole line or change it from false to true) Steps Edit the 'purgecachespage' lang string in lang/en/admin.php to the following: $string['purgecachespage'] = 'Purge caches (Edited)'; Log in as admin Navigate to Development > Purge caches in site administration Under Purge selected caches select Themes and press Purge selected caches Confirm you see the message "The selected caches were purged." Confirm the theme cache was purged (the name of the folder within <DATAROOT>/localcache/theme will reflect the time the cache was purged) Confirm the string cache was not purged (page heading should still read Purge caches ) Ensure Purge selected caches > Themes is still checked Press Purge all caches Confirm you see the message "All caches were purged." Confirm the "Purge caches" heading has changed to "Purge caches (Edited)" (i.e. all caches were purged, not only the selected themes cache)