It's worth noting that sometimes the spellings are the way they are purely because of copyright issues or mistakes. Mithril is from Tolkien - and it's clearly what the Japanese writers intended. But whether by mistake or through fear of being sued, the i became a y. Ochu (correctly Otyugh) is definitely deliberately misspelled in the English games over copyright fears (Alex O Smith told me). Also the motorbike-like monster "Hell Harley VR2" became "Hell Rider VR2".
Sometimes, even fear of offending religious people has had names change in the English version. Cid's Weapon, Longinus (which is itself likely a mistake on the Japanese writers' part, since that's the name of the person who stabbed Jesus and NOT the spear) was renamed "Spirit Lance". https://en.wikipedia.org/wiki/Holy_Lance
You can see here that it is never known under that name. It's always "Holy Lance" or "Holy Spear" or "Spear of Destiny". It's very strange to me that Baskett, or someone else at Square America, understood who Longinus was and amended it.
On the Midgardsormr - this "swarm" business is purely down to the localizer not knowing the mythical beast or how to spell its name. They see the kana for "sormr" and think "Shit. What the hell is that?" Not realizing that it is Old Norse. Luckily, later revisions of FF games have tended to use the correct spelling. It's also worth noting that they often use the alternate spelling in the Japanese FF series - Jǫrmungandr. This isn't the case with FF7. Furthermore, this "Midgard" issue confuses people - they think it's named that way because of the city of Midgar. This isn't true. It's just that in Norse, "Midgard" means "World" - and the city was named after this (but they dropped the d). With the creature, no change was made whatsoever. They shouldn't have used "Midgardsormr" in FF7... they should have gone with Jǫrmungandr, and that would have avoided any confusion.
On Morbor - it definitely isn't Malboro - but that's the most common name given to it in the English localizations. Worth noting that FF11 did differ and went with Morbol. Judging by the fact that Morbo means disease in Italian/Latin, I'd say that's the real origin - but that the original designer of the monster simply added an r to the end. It could still be an l at the end though, but without the original creator saying so, we will never know. I understand that in this case, this project is likely going to go with Malboro, since that's mostly used.
Finally, Cloud's ultimate Limit skill "Omnislash" is actually closer to "Super Ultimate War-God Supreme Slash" - which obviously I ignored for my own sanity. But more interesting is the fact that "Omnislash" ended up being used - in Japan - in at least one FF7 spin off game (I can't remember which it was). So, evidently, even they thought it was bizarre and elected to use the English version