Honestly, the region shouldn't matter. If you want you could add a little notice that it's English-only for now, but there's absolutely no reason to limit this to a particular country. It's a totally free service and it doesn't involve complicated region-specific licensing agreements, so where someone lives quite simply does not matter.
I hope you are aware of the fact that language and geography most of the time don't match because one person is capable to speak/read multiple languages and that English is understood by people outside of the USA?
Other than "every", what language or regions would you want/expect/need first?