Since multi-lingual handling in Joomla is now essentially separate content that you simply map to a language, all you need to do is simply create separate extra field sets (groups), map them to separate categories and accordingly to separate items.

In other words, you create content in German, map it to categories designated for German, with associated extra field groups for the German language. Repeat the same for French.

Since content from extra fields is tied to each item, you would never see a German item with data from the French equivalent.

The only thing that is missing from K2 is a way to map cross language content (associate translations). In other words, when you visitors read item X in German and then click the language switcher for French, they won't get the translation for that item but rather be redirected to the French home page.

But this will be launched pretty soon (as in next week) in the form of a new K2 plugin. This plugin allows you to easily associate one K2 item with one or more in other languages, so language switching in the frontend is transparent to your visitors.

Good thought Okan ;)