Confusing region keys

I've seen EU and US keys advertised out there. What is the difference between the two? Oh and and the JP key too. I heard the US and EU servers are at the same location?

1. Do all of the keys allow play using the English language?
2. Can I play on a server that is not of the same region (eg - EU/JP server using a US key)?
3. Do I pay for subscription in the currency of the region key I activated (say, in the case of a US player who used a EU or JP key)?

Thanks in advance for the clarification!

1. Yes
2. Yes
3. If you created a US account you can only use US key! Sub wise is the same.US pay USD. Jp Yen. Except for EU. UK pay in pounds but everybody else Euros.

Thanks for the information! Now I know what copies to get when digital sales reopen.