I just tried to register with Zanata, and got this message:
Maintenance-only Zanata Instance
This service is in maintenance mode and new projects are not accepted, sorry.
Since the upstream Zanata project has been unmaintained for quite some time, we have decided to continue supporting existing projects as much as possible but refuse new projects. Adding new language coordinators is also not possible, although if you've been around for some time we might add you as reviewer to ease the situation.
Another translation service is Transifex.