[matijao]

In Croatia it's "ipsilon"

[coldtea]

That would be its ancient Greek name.

It was one of several "i" sounding vowels (like english has: i as in bin, e as in be, y as in gym, etc, roughly sounding the same).

"Y" has "i psilon" meaning "high i" (literal) or "slim/bare i" (referring to how it was pronounced).

[erutuon]

Psilon in this case means plain or simple (as opposed to compound or two-letter), as in spelled with one letter, because when the name was coined in the Koine Greek period, υ was pronounced /y/ like οι (but not like ι as in Modern Greek yet). Similarly, epsilon (ε) was pronounced like αι (as it still is).

[askonomm]

In Estonia it's both Igrek and Üpsilon. That said, the letter is not in Estonian alphabet and is considered a "foreign letter".

[airstrike]

Also in Portuguese!