Hi Alexander,
What you suggested is almost what I did.
This is what I did:
1) Created several TAG GROUPS, all with same group name + culture code ( tagName_en-us etc.).
2) on BLOG main page- > metadata -> selected "Page tag group" for this culture.
3) ALL blog post INHERIT that tag group
4) cusotm webpart properties using TAGs ->
-> WHERE CONDITION : {% CurrentDocument.DocumentCulture |(identity)GlobalAdministrator%}
-> in actual query: Where TagGroupName = N'Blog_##WHERE##'
Thanks for all your help