i18n files should have test that check if keys are fully common between them

We should add a test in meteor tests (that run in pipeline!) that check if all the i18n files (at the moment we only have FR and END) have same exact keys. With a fully deep nested approach, check everything.

It will NOT prevent translations errors, but will assure we do not forget a translation in just one file.

At least it will show something, not the slug like "pages.about.title"