Curate the list of languages in Tails Greeter
We currently have many languages or languages variants that are poorly or not translated at all (either in Debian and GNOME in general or for our internal tools). It's the case for example of "Chinese, mandarin" and probably many others.
Having such a long list makes it harder to know which languages are actually well translated and for the user to know what's her best option is, without trial and errors.
I think we should filter this list to only display the languages that are reasonably well translated.
If we base ourselves on the PO files for our internal tools, we might be able to automatically generate a list of languages during the build. Making sure that our internal tools are well translated in a given language before listing it sounds like a good criteria too.