LexiconHelper is a utility to assist add-on component developers in internationalizing their components.
It compares code files against language files and reports missing,
empty, or unused language strings. It identifies language strings in both code files (snippets and plugins) and in property files.
Best of all, the display of missing language
strings can be pasted into the language file for completion.
Note that this is a tool for add-on developers, not translators.
Package:
http://modx.com/extras/package/lexiconhelper
Tutorial:
http://bobsguides.com/lexiconhelper-tutorial.html