Re: Users need to know that
It's a feature, sort of, in that it allows someone to link to a translated page rather than its original. Instead of requiring each user to know that you can go to translate.google.com and put in a URL, you can directly link. For example, this article translated to Spanish gives the following URL, which doesn't have google.com in it because they have their vanity TLD and they're going to use it:
This format is more obvious about where it's going, but the old format did all of it with query parameters and probably still works. The user needs to know that something starting with translate.google.com doesn't mean Google approved the content.