Did you copied it to the module folder?
program files/mountblade warband/modules/dev1257/languages
It should work fine... what revision are you playing?
Yep, it's in there.
Version is 1.153, but I was told that it would still work fine.
EDIT: by the way, I'm using the SVN version, if that's what you mean - I have a feeling it's what you were asking, since, in the language folder, 'en' is the only one that doesn't have a tick by it.