Problem here (for me) is that my answer is dependent on the situation.
I like playing with non English speaking players as well, BUT I would gladly through away this for more responsive servers.
Hated never being able to land stun in FFXI.
I literally casted it BEFORE the readies WS text appears, just to prove how impossible it was for me.
I cast Stun, Enemy readies WS, it says enemy is stunned, and the enemies WS goes off.
OR, I see the text, hit the button (w/o delay, as I showed my friends in a video how quick I was.) see the spell either tie with the enemies WS going off, or going off after their WS.
Eventually I gave up and just spammed Head Butt as BLU on most fights (w/o built resistance.)

EVEN if they manage to lower the lag, the fact is, if its even 0.2 of a second different from JP players, they will base content, such as stuns or w/e, around the JP players times. Otherwise the JP players would have less of a challenge.

So if it would fix server lag, I'm willing to go to an all English speaking server.