We use WHMCS for our billing in our hosting company, and we've had a couple of non hosting companies use the software for their recurring billing also (Gym membership, wine subscription site, etc). The software does allow the changing of languages on the user interface, however I believe the admin end all stays in English. We deal with international customers daily, and haven't had anyone complain about the language in the client end of things as of yet.

Might be something to have a look at also - (www.whmcs.com)