I don't really know whether my Terms of Service section should be in English or in German. I first thought obviously in German, because I live there and German law applies. But how should people who don't speak German (and these are 80% of the traffic) read this section?
Should I write the ToS in both English and German, just to be sure?
Of the 20% who do speak German, do they also speak English? If not, and 20% of your users don't speak English but instead speak German, then I'd think you've got a pretty large group of non-English visitors. It would make sense then to serve those visitors with T&Cs in their language (English and German). If everybody speaks English, or almost everybody, then probably not a concern.
Are you using a translation service (like Google Translate) on your site? If so, what percent of your traffic translates your site into another language? If any group is sizable (like say, German), I'd offer up T&Cs (and other content!) in those languages along with the English content.
On any content you offer up an alternate language for, be sure to use hreflang: https://support.google.com/webmasters/answer/189077?hl=en
