"We went traveling in Germany in July last year."
Ive always been taught 了 can be placed after the verb OR at the end of the sentence as long as the action has finished. My answer of 去年七月我们去德国旅游了 would be right right?
I agree too, I don't see why going 去 can be a completed event in this case if 旅游 isn't also a completed (and past) event. So 了 should come last.
If 去年 is mentionned, do we absolutely need 了 after 去？
Once again, it is impossible to tell what Duo Lingo wants in terms of the order of subject and time. 我们去年七月去了德国旅游 is perfectly grammatical Chinese. It should be accepted. But the larger issue is that in these exercises sometimes the subject coming first is "correct" and other times the time adverbial expression coming first is "correct." In fact, both are correct and should be accepted, or there should be some very clear explanation or indication as to which is prefered.