Pull updated translations from Transifex.
Add mn (Mongolian) language.
Do not update English translation for now as we want to keep
compatibility with 0.9.
Last update (48be9ce) missed quite a lot, for some reason.
This is also the first update done with the new script
`contrib/devtools/update-translations.py`
Adds three new languages:
- de_AT: German (Austria)
- gl: Galician
- sl_SI: Slovenian (Slovenia)
Updates many others.
Thanks to the translators contributing on Transifex!