Having a one-language site and multi-language blog using the post categories!

Hello folks!

Situation:

1. I basically maintain all sites in one language (en) and the main blog in one language (en) –> so usage of standerd wordpress is sufficient.

2. Now I want to be able to post in two additional languages – but not the same content as in the english blog. E.g. I’m currently learning a new language and I want to use the blog to force me to write some stuff, but I do not want to translate the whole stuff I write in the english blog.

This is the idea:
Introduction of 2 categories (e.g. “german”, “greek”) , which can be used to filter. So in the main blog page no posts are shown which have either of those categories. In the “german” blog I only filter the posts which are in category “german”, etc…

Do you think this is a proper idea?
Or is there already a plugin which allows something like this?
Regards,
mydani