After having seen many CAT-Tools only one of them allows to properly localize .po files, supports all ISO 639-3 languages and is multi plaform: Virtaal
Vox Humanitatis over time is going to care about the localization of the Gnome UI in various less resourced languages, all of them ISO 639-3 languages. A tool that can be used by translators who mainly work offline was needed. The choice fell on Virtaal thanks to its features and a very intuitive handling.
This means that we of course also support your localizing Virtaal itself.