The line shell_out("git -C {} checkout {}".format(directory, branch)) is throwing an exception as the 3.7 branch does not exists in french translation, this is expected and don't crash the script. it just don't compile the unexisting translation.

It should be reported nicely instead of logging a whole stacktrace: misreading it the first time make me though the 3.7 english build was failing.

I'm currently fixing this.

Thoughts: I should probably build an untranslated version using po files from a near version… so if a new version spawn, we don't wait for translators teams to push the branch to build the docs.