A button (or another way) that let's you jump from one specific message in the wiki into its corresponding TranslateWiki message. Maybe a way to access TranslateWiki from the wiki itself without actually going to it?
Useful for finding and translating system messages fast in general.
I'm going to decline this as not everything might use translatewiki.net and as this does not sound like something to include in MediaWiki core or an extension.
You are free to write a custom JavaScript which checks the URL for uselang=qqx and then automatically appends links to each message ID, if wanted.
See https://www.mediawiki.org/wiki/Help:System_message#Finding_messages_and_documentation
@Peachey88: This is nothing to implement on translatewiki.net itself but something to display on other wiki installations, hence removing the unrelated tag.