There were several multilanguage server, with Russian language, German language and Spanish, if Im not mistaking. They had some success, but they never were such popular as Disco GC.
Both of Russian servers had many problems, such as capspam, megatons of hate (more goes to Siberia Optizone) where player were involwed into open confrontation between each other, and stuff like it.
And another point, with donors (if I understood you correctly- you mean players, who will join GC server, after playing on paralel server?)
Idea is not bad at first look, but.
1)New players will rather go here, as server with max players.
2) Players, who have played on another server, and have gained lots of stuff, like multiple battleships, lots of Code weapons and so on, very unlikely join another server, and start everything from 0.
3) Players who played on parelel server (with probably diffrent rulest, and defrent RP enviroment) could find GC server unpleasant for them to play here. ( We know our internal problems, Im sure, that there is no need in listing them here now.)
4) Players who played on parelel server (with probably diffrent rulest, and defrent RP enviroment) could be "badly integrated" into GC server, causing more problems and negative effect, rather than positive. This will be going until first seriouse sanction. Usualy, player will just say "S***W YOU ALL A******S!" and just left server.