What engine was fallout 2 made on. Ive looked everywhere and couldn't find it.

Wikipedia states it uses Fallout Engine, same as first Fallout (upgraded version of it at least). Everyone else seem to call it that as well.
If you want to know anything specific about it or it's internal workings, best place to ask is Fallout Modding Forum at NMA. There's also Vault-Tec Labs Fallout Modding Wiki that has lot of information about various file formats used by Fallout games.

It's based on the Infinity engine, the same engine used to make the Baldur's Gate and Icewind Dale series for example.

Where did you get that idea? Fallout Engine predates Infinity Engine and uses entirely different file formats. Also according to Wikipedia, Bioware designed Infinity Engine specifically for Baldur's Gate.

what language is it coded in?

Urh, that's a difficult question as game engine (exe) is a compiled binary file. My guess would be C/C++. You should ask at NMA modding forum if you want to be sure as they've decompiled/disassembled and figured out large portions of the exe functionality. Why do you want to know?

curiosity.