It looks like this extensions hasn't had any code maintenance in the past 7 months. I doubt anyone will look into this. But we have Nemo_bis, I'm sure he'll try to chase a developer.
From what I see from grepping, this message doesn't seem to be used.
I reopened the issue, as it appears no code changes were made to actually remove the message key from the i18n file. As a consequence, the message is still open for translation, so the issue is not resolved at all.