Update English localization file

Hi!

So here're the edits I promised you in #256 Sorry it took so long, and please check it 'cause I finished in a bit of a haste and could make a few errors. I think I'll also re-read it myself tomorrow evening to make sure I did good enough job.

Oh, and one note I wanted to make: when talking about pets, English people use "it", not "he/her" (or should do so, according to rules). It's fine to use "he/she" to show the affection, though. Should we do something about it?