It just occurred to me that if I'd gone to the "Night before the Oscars" party, Linus would have been the only one I'm 100% certain I would have recognized and been certain about his name.
This goes far outside of just the Latin-derived languages. We use the Latin alphabet, after all. So if the language can be written with this alphabet somehow (even if the locals don't usually use it), there's a pretty good chance that you should assume they use the Latin vowels, too.
No guarantees, but I've managed to surprise more than a few people by pronouncing things correctly.