Steven, I'd recommend not to change that message because it is correct
and you can understand easily what it means. German phrases are
usually longer than their English equivalent, so that's all right (the
German translation of an article from Scientific American can be two
pages longer than the English version).
In this case the phrase is not equivalent, but was expanded beyond the English version. The original English is: "Help me choose" and it is right next to "Username". The default German translation is "Auswahlhilfe", as you can see on German projects other than Wikipedia. As you can guess is short enough to not overflow in to multiple lines. In general, the purpose of the link is not to provide a general help guide to signing up, only to choosing a username.