Improve i18n support

Currently you can already chose the language of a specific tag, an the original tag from which is was translated. But thats not enough. We should either make sure, that the translated tag will copy all hierarchical and synonymous relations from the original tag, or adapt the search, that also these field is considered.

As a current workaround, you can just add the original tag as a synonym. But i think, for later it would be nicer to have different language trees.