I just wanted to clarify that the OTP client in the src/client directory has not been updated much recently, and is not used in production by most of the larger OTP contributors and deployments. A lot of current contributors refer to this as the "debug client" which is conveniently bundled with the OTP API server, but not used in their public deployments.
Therefore it's possible that contributions to this client would mostly be seen by developers and small test deployments of OTP, and might not appear in public deployments. You are of course still welcome to work on translations, but just be aware of the usual use case of this client.
Regards,
Andrew