I wouldn't consider Tatiana 'foreign'. I'd see it as either a little posh/upper class or Shakespearean. I like the name.
Isabetta is not a name everyone will love. Personally I think it's feminine and attractive. It's a nice (and much more original) twist on Isabella, and it has some cute potential nicknames (Betty, Isa).
Please not Tatiana, it is a slang word for Jezebel! If she is going anywhere near a south London secondary school, please don't! I don't know if it's still a thing but it certainly was less than 10 years ago. I quite like Isabetta. How about- Iseult Carlotta Katrina Alexandra
Tatiana is... I don't like it. Isabetta is really lovely. Although I personally do prefer Elisabetta or Isadora... But it's really nice. Vittoria, Alessandra, Clarissa, Carlotta, Andreana, Aquilina, Antonella, Leandra, Giuilia, Liliana, Marigona, Leontina?
Interesting. I like them both, but never heard of Isabetta. Where does it come from, and is it that country's version of Elizabeth or Isabella?
The only thing against Tatiana is it sounding like 'tatty' (= dilapidated or poor quality object), but maybe that's a word that isn't used much now? Anyway, most names sound like something else. As a name it's beautiful, makes you think of a Russian princess.
I'm not keen on Tatiana but love Isabetta! Very similar to the Scots name Eisabeth (pr. Eezabet or Eezabeth), which was hugely popular in the 17th/18th centuries. I'm desperate for someone to revive it!