http://www.wowprogress.com/realms/rank/eu is your best bet to check faction balance and pve activity. It basically computes how many people have killed a raid boss per faction. If you click a realm you can see the guilds and check yourself what language those guilds are (e.g. burning legion as always had fairly balanced factions, but pretty much every guild there is Polish).

Cross realm zones mean that in the 1-85 zones you will meet plenty of people of the opposite faction. Basically battlegroups share the 1 to 85 zones. Now they are even in the process of merging low pop realms as well (as in sharing everything, from chat to auction house). But it might take a while before this is completed (connected realms is the term blizzard uses).

There are very few balanced English speaking realms who have a decent population and have a good pve community at the same time.