This thread blew my mind. Seriously. Glad to offer more international inconsistency fun!
So, Russian vowels are not differentiated by their length, i.e. there are no long or short vowels at all, each vowel can be both with no difference in meaning. When speaking, people tend to pronounce the stressed vowels longer for better emphasis. The position of the stress can shift in borrowed words or name adaptations in order to make the word more pronounceable. To make things worse, Russian consonants are divided into hard ones and soft ones. Add to all of that the fact that Russian localizers often had no idea how to read a certain name, which resulted in unpredictable variants.
Aeris/th -> EYE-riss
Tifa -> TEE-fah
Yuffee -> YOU-fee
Cait Sith -> Kite Sit
Rufus -> ROO-foos
Reno -> REN-oh
Elena -> yeah-LEN-ah (a common Russian name, by the way)
Poor Tseng was just translated letter by letter, hence /tseng/.
Sephiroth -> sef-ee-ROT or sometimes sef-ee-ROSS (because we don't have the 'th' sounds)
Jenova -> /ʒə`nɔːvə/ (pretty much like 'supernova')
Mako -> MAH-koh
Materia -> mah-TEH-ree-ya (luckily, this is an existing word over here, so one problem less)
Mythril -> miff-REEL (as I said, translating the 'th' sounds is always a pain in the backside)
Nibelheim -> nee-belle-HIME ('belle' like the French name Belle, lol)
Mideel -> mid-EEL (with the soft 'l' at the end like in Belle again)
Midgar -> mid-GAHR
Wutai -> voo-TIE (there's no /w/ sound either)
Corel -> KOH-rell
Gold Saucer -> translated literally into Zolotoye Blootse (why does it look so hilarious omg hahaha)
Gongaga resembles my hometown Kaluga (kah-LOO-gah) just a bit, so gone-GAH-gah.
Surprisingly, the way I got used to pronouncing all this stuff peacefully co-exists with the way I hear it's pronounced by Japanese and Amerian VAs, like in parallel universes in a way