I don't live in Horsham but I go there every 2 weeks or so as a friend lives there. I lvoe it - it has the big shops but also some litttle independent ones too. lots of old buildings, little squares, lots of greenery. Library, pool, bowling alley, theatre, park...all lovely.
As far as I know, the schools and college are excellent; my friends dd went there.
It's on the main train line to london vis gatwick, and everywhere is accessible from eiither ofthese.
It is pricey tho, although villages outside Horsham are cheaper. There are regular buses.
Another place to considr is Horley. I live in Horley, right by gatwick Airport; great for access to London/Brighton/anywhere by train and also by motorway. And of course everywhere in the world by plane! House prices here are slightly cheaper than horsham, and schools good. Colleges are local, in Reigate, Crawley and Redhill.
Can't comment on the % of non-English speakers tho, I think with the amount of people working at Gatwick, it's probably higher than 'normal', though I've never really noticed. I think I'd consider it a good thing, anyway, as I speak 2- other languages myself.