add i18n specs

I same test for the i18n locales, this test are failing until #3518 and #3524 are merged.

The tests validates each locale file and checking it against the en file.

The benefit of this test are that we can see this things:
* a developer add some keys for thirdparty gems
* the locales are invalid
* have the wrong namespace / iso
* a developer add some keys for a feature only in his language and not in english