I'd say the population is as balanced as it's going to get. F2P shifted it heavily towards Empire, though. Was playing Dromund Kaas the other day, 7 instances, with 6 of almost-full that comes in at over a 1000 players on the planet. Fleets are more occupied on the Empire sidee too, but I except this to tone down after a while. Warzones are fairly balanced as well, I can go with streaks of wins and losses for some time, though I seem to be winning about 90% of low-lvl warzones, on either side.
Oh, and yeah, general chats are prominently in English. Mainly guild-adverts are seen in other languages, and sometimes (although rarely) a conversation in another language bursts out, but they are usually short and people often stop if asked to.
Low level warzones is a complete joke on the republic side now, I have been playing hours and hours every day since the launch of this game, and this, since free to play is the worst ive seen when it comes to bad players so far.
Ive done around 60 warzones since free to play. just pugging and ive got now maybe 5-6 wins
when all these guys reaches 50 , if they do, im sure it will impact the republic 50 pvp in normal warzones very negativly.