The Combiner Wars set went with "Fellbat".
The WoW fan in me appreciated that and wish they'd have kept that as his Western name.
So what's the excuse for "Leozak", "Jaruga", and "Gaihawk"? All of them are misspellings too, of "Leozack", "Jallguar", and "Guyhawk".
I have no idea, but here are my best guesses.
"Leozak" was probably seen as a more "concise" spelling of "Leozack." Sounds the same, but it's one less letter and someone may have thought it looked tidier.
"Zack" is also a common variant of the name "Zach" and I can see someone at Hasbro not wanting Transformers to have human-looking names, so "...zak" is preferable to "...zack."
That also explains why they went with "Gaihawk" instead of "Guyhawk," with "Guy" a fairly common name.
"Jaruga," on the other hand, is a mystery. It doesn't do anything different than "Jallguar," like replace a human name or get rid of a word that might offend someone. It's just different for the sake of it.
Best guess is someone didn't like "Jallguar" and wanted a different name for the character's "official" Western release.