For example another store forced me to buy a regional version of a certain game which is a bit different (doesn't support modifications) and I'm wondering whether I get the same version if I pay less? Thank you.
I attached the different store pages for Morrowind. So is that the same game I get?

Both screenshots are from GOG; right? If you buy a game as a gift you always pay base price, no matter where you are. If you buy for yourself you pay whatever the price is in your region. Could that be the explanation for the discrepancy between the screenshots?

Probably this.

I should have used the game I haven't bought yet as an example. So the question is: do I get the same version of a game I buy for a reduced price?
Does GOG put different price tags for the same game or it's a different version published by a different company? I probably should be more specific: New Vegas RU doesn's support mods and the regular version does so I'm ready to pay full price but if the setup file is the same for everyone it makes no sense to pay more.

I think I heard that occasionally the game can differ depending on what language you choose to play it in, also mods and fan patches might require certain lanugages to work.

Price paid matters not.

It doesn't matter for this thread, but this is not correct. You don't always pay the base price for gifts. You always pay at least the base price. If you are from a country with a higher price than the baseprice, youll have to pay that (and of course get the difference in store credit).

I've always seen it like that the wallet funds are good enough to consider I'm paying the same. But yeah, technically you're correct.