leaving 行きたい like this sounds a bit childish. japanese people add とおもいます after いきたい to imply that is their thinking. ロシアに行きたいと思います。
So Tai is also want? what about ga hoshi?
ga hoshi is used for nouns, tai is for verbs (^ ^)
Как будет "хочу уехать из России"?
Why not へ instead of に?
You use 'ni' because you have a definite location, with 'he' it would more or less mean you want to head in the direction of russia.
So the formal version of 食べたくない is 食べたくありません, right? Is there a formal version of 食べたい? Or is it informal and formal...?
Why not ロシアに行くのが欲しいです
Not confident with this reply, but I'd guess it's because, as in English, it sounds weird to express desire for a nominalized verb. That translation would be like saying "I want going to Russia." But again, could totally just be a Duo thing.