UI or page to find out where a translation is defined

As a developer or even as a would-be contributor, I find it non-trivial to track down where does a translated piece of text I see on the wiki is coming from, so I can either fix it or translate it for a new language.

Translations can come from either ApplicationResources.properties files, wiki pages marked with the XWiki.TranslationDocumentClas xobject (at multiple global/wiki/user levels), wiki-level registered document bundles and they can get confusing really fast.

It should be doable with the localization module and a UI should exist to allow searching by translated text (much like l10n.xwiki.org has) or by entering a key an seeing where that key and its translations are defined.

This could be seen as an analogy to the XWiki.WikiMacros page.