Who admits new Transifex Translators?
Currently Transifex has a setting to automatically accept new team members, but it is a global setting, not per language.

My recommendation would be to use the "reviewer" feature of CiviCRM. If you tag strings as reviewed, only reviewers can edit them. You can then more easily review strings that have been translated by new translators.

I agree, however, that it would be nice to have a better welcome process for translators. Currently the only help we have, is the text shown on the main CiviCRM Transifex project page, which says "help page" and leads to Translator Resources.