What happened when I tried to join translatewiki.net
I recently registered to translatewiki.net. I just wanted to start exploring it at my own pace. When I realized my initial status was "an unapproved translator" I wasn't sure what that meant, and I figured I'll submit an initial translation sometime later. I was unaware that timing matters, so I was planning on doing this on the weekend when I have more free time. On Friday I received an email saying "I have rejected your application, because the quality of your translations did not meet the requirements".
This was confounding to me as no translation was even submitted yet. The email didn't say so, but I think that the issue was not with the quality of my work but with my timing: the fact that I didn't post something right away.
What I recommend
A more user-friendly approach in such cases would be to send the candidate a reminder email asking them if they still wanted to contribute, and clearly informing them of the time window. If a new user must submit a first translation for review within a certain time frame this should be stated prominently before a rejection email is sent. Otherwise this makes for a needlessly bad user experience.