Who know about Firefox, please come in

I don't know what's the language edtion of operational system you used? If u use non-english such as Franch, Japanese, etc. whether the firefox you installed would follow the language of your operation system? I mean, if you use Rumanian language system, then even u download firefox in English web, the firefox will still show you Rumanian firefox, not English?
If so, how can I use a English Firefox without changing my system?

I have Windows XP in Portuguese and Firefox in English because the Portuguese version was a little older (now they have updated it). Also, I usually do not like the translation.

Firefox has different versions for different languages.

You can see it here.

I prefer Opera, and Opera lets us change the interface language, we can even alter the text as we like.