Thank you for taking part in translating Transmission!
As with any other project, we expect you to be familiar with particular Transmission client you are about to localize, and localization practices and guidelines related to specific UI toolkit (GTK+, Qt) and/or operating system (*NIX, Mac, Windows), let alone the terminology used by your audience / our users. We expect some level of commitment in that you not just blindly translate the phrases but also hopefully check your work by running the particular program to see if phrasing matches the context and layout isn't broken as a result of your changes.
General rule is that new localizations are only included in next release if they are at least 95% complete. Transifex (see below) offers a review functionality, so if you feel like it and are not afraid of responsibility — don't hesitate to ask and we could then have a different deal based on reviewed percentage instead (nothing is set in stone as of now).
Translations for Mac, Qt and GTK+ clients are managed on Transifex. To help localize, or add your new localization, you'll need to register on Transifex and join the translation team for Transmission project.
GTK+ client translations were previously managed on Launchpad, but this is no longer the case. No phrases will be updated there, and none of your translations made there will be integrated back into Transmission.