My Board is mostly being used in German but there are also guests that use English as their default language. Is there an AddOn out there that shows a flag in the category so people can see quicker which language the post is in?
Well, sorry to hear. Then you should create seperate categories for each group. So English speaking people has their place and German ones their.
And/Or use User group promotions based on user language. So you can hide all categories were German is used, if someone uses English to surf your site.