Hello,

There is a German translations. However Firefox decides what language it will use.
If you use English Firefox then you will probably have to force it:
1) open "about:config" in Firefox, and search for the "general.useragent.locale preference"
2) double click on the preference to select it, enter the language code "de"

I hope this helps,

Have a nice day :)

Best regards,

Juraj Mäsiar