Disappointing. I didn't think for a second that I'll say it, but so far my experience with transifex is really disappointing. If it wasn't for opentranslators.org I would not bother with them actually.
First of all let me say that I value what they try to do! I know that it is not easy to satisfy everyone and I also understand that my disappointment is largely connected with the fact that I'm new to the platform. In the next few paragraphs I'll share my experience hoping that I can save you from losing 2 days in trying to upload your extension translation files to transifex. I also hope that this blog post will be of use to transifex and it will help them improve their system.