Yes, I agree with you! I tried this extensions's front page link (in the green box) Translate the ExternalLinks extension if possible but there was not translation for that in translatewiki. I'm not yet familiar how to add a translation there.
Many times when you click same kind of link on other extensions, they straight open the translatewiki.net page on your language and you can straight start to translate. I supposed, there is not any translation of this extension and that was my reason to do this way. If I find a way to do it in translatewiki, I'll be happy to move them there.