That's a bummer when the phone doesn't have the language you need. As far as I know, T-Mobile doesn't have any specific plans to include any additional languages. Other folks have asked about this in the past and it's something that would need to be created by developers.
ZTE has almost dropped support for this phone. It is no longer on an update radar. It has reached its end of life already. Security patches are all that will be received if and when ZTE approves.