Thread:AgentMuffin/@comment-31427784-20180720023314/@comment-25653892-20180720030040

You can view messages like button text by appending  to the URL. Using this, I found that the location of the locked Edit button text is at MediaWiki:Oasis-action-viewsource. This should also work with every other message stored in the MediaWiki namespace.

The custom masthead tags are applied through an add-on at MediaWiki:Common.js. An active admin will want to follow the syntax of the existing code to create new tags.