@Gina it's worth noting that Fosstodon *became* an English only server; it didn't start as one. When it changed, there was significant backlash.
Translation services are good enough for moderation, plus there's always the option of starting dialogue with a person to better understand context. I spoke to that somewhere in the thread, but other admins have come out and said the same.
The only limitation is in willingness. Telling someone to GTFO as Kev has done, only shows hostility.