I've modified an Astro 320 GarminDevice.xml to Alpha 100 and changed in it the French text version to 2.00
Webupdater gave me the 2.10 version for Alpha 100, there must be no French 2.20 version available.
All other available languages are 2.20 version (except Polish 2.10)
cslrGg
Check your GarminDevice.xml and search for gtt
If you don't find any entry about gtt, then maybe your american Astro 100 doesn't support any other languages.
Do you already have other languages except US on your device or not?