As someone whose grasp in Japanese is only as good as Google Translate's and, unfortunately, has grown tired of trying to tackle end-game in 280+ ping environment...

Objectively speaking opening an 'EN-only server' in the JP datacenters, as sensible as it is in a debate about practicality and functionality, I personally don't see that happening anytime soon, so I'll have to echo Xeta's answer to an extent - you'll have to be happy with getting into alternative 'English JP-servers'.

If you'd rather have a more established population than Kujata/Typhon, Masamune also has a pretty healthy number of English-speaking population, though we're not in the same DC as Tonberry :c We're not on Tonberry's level where even the map/hunt shouts are all in English nowadays, but finding an English fc that's not dead isn't an issue at all in masamune.