I am aware

But my tongue just takes up all space in my mouth if it isn't closed

Is this where accents come from?

If you're french, the tip of your tongue is supposed to be at the top of your mouth

I have my retainers in my mouth, so I have no idea

What about Hispanic? And I'm bilingual

You are now aware of your own tongue.

HELP NEEDED! Can any native speaking Russians confirm this?!?

mine goes between my teeth

im not russian tho ( nor do i speak any of their language) and still my tongue's resting at the bottom

Both: At top

Well I'm portuguese and it is pretty similar to russian and yes it sits at the bottom

Danish needs the tounge to stay roughly in the middle, and occasionally going all the way out to the lips when we pronounce soft D's. Norwegians and Swedes say we sound like we are talking around a potato in our mouth for precisely this reason.

It's probably the language you're more fluent in. Or whatever language you're speaking at the moment