Add L10N support (fix bug 841066)

I think I may need an l10n-knowledgable person to help me out with
.pot > .po conversions or whatnot so this can be translated by folks.

@fwenzel, any recommendations on where to look in playdoh to do the .pot > .po dance? I don't quite understand gettext, but if I can get .po files there's a tool I can use to change them into JSON, which my client-side library will :heart: