Deleting Russian Language Invoice


Since I am using 3 languages in my website, there is a situation, where, when user is ordering something in Russian language, he receives invoice in Russian language too.

Problem is, document in Russian language is not valid and never will be valid, so I need to either delete Russian language invoice, or rename fields. All I want to do, is to make only 1 invoice language valid and set as default.

How should I do it?

Regards, Vairis