Thread:Project:Support desk/User Preference descriptions - Where stored & changed, and where documented? - How to mark the "defaults"?/reply (6)

Grepping the source turns up includes/Preferences.php which has about 40 messages that begin with 'tog-'. You can find a few more starting at line 647 of languages/messages/MessagesEn.php.

If all you want to do is modify the labels, then add an "i18n" tag to your bug report and get some input from User:Nikerabbit, User:Siebrand or other people on the i18n team.