In the US, when you need to present proof of identification while using your credit card, can a foreign ID...

Question

be used? Especially a non-english ID (Finnish driver's license for example)

Answer 1

Don't think, especially if they can't understand the language. A passport would be best but then there are some idiots out there who don't even know what that is.

Answer 2

Probably not --- and not because it should not be valid proof.  What usually happens is that, confronted with a foreign document, the person requesting the document will simply "flip out" and deny it as a valid ID since he or she is not confident enough to allow it.

My wife and I also married in the USA to avoid the constant problem of presenting a foreign marriage certificate as proof of marriage.  Also, my wife, who is now also an American citizen previously had little luck using her Mexican passport or voter card as IDs even though her photo was on them.

This is one of the difficulties of visiting an undeveloped (as opposed to underdeveloped) country.