As a general rule, only creators of extensions are allowed to submit their work on the Web Translation System.
Thus they can keep control of their releases.
But it may happen in some cases that a developer gives the explicit permission to someone else to submit and manage his/her extension(s). 
It must be very clear in these cases that the person in charge of the extension has to be fully authorized to do so and will report to the creator at every necessary occasion.

For more information, please see the other Questions & Answers