I was searching for a plugin/gem solution to extend the native rails i18n for storing my translations into my database. Maybe I used the wrong search terms, but all I found
it has a DB-backed backend that comes with a controller to do the translations over the web.
The caching is built-in, though we had to code pre-loading of all of the translations on boot (it is much faster then get them one-by-one with caching).