Translate the Primerpedia interface (i18n)

[waldyrious]

A simple approach could be to store a config file in this repo (as suggested in #38) for the strings that would need to be translated; this will probably be a quick way to getting a functional multi-language site off the ground.

Eventually, we will want to set up the translation on TranslateWiki, rather than rolling out our own translation system in this repo. That's tracked in #47.

(Edit - just fixed a broken link)