Languages limited with store_id [help needed]

I'm running multi-store system on oc 1.4.9.3

I have added field 'store_id' to table languages in database and modified catalog\model\localisation\language.php with where clause to limit languages to current store_id. Frontend works just how I wanted; only certain languages are visible for each shop.

My problem is that now admin product section shows only languages where store_id=0.

As a php novice who just figures things out by trying hard, I'm really stuck with this.
Any help highly appreciated.

I looked closer at my problem and it seems to be language cache what causes this.

If I clear language cache, system works fine where ever I go first (admin or front). But after that I suppose it reads language from cache and then it's not like it should anymore..

No one?

Someone?

Does anyone even know where to find some professional help to solve this kind of issues?