Translation:I spoke in Portuguese, but he could not understand me.
I feel like most of the sentences in this lesson have really bad English translations :/ If "I spoke in Portuguese", that means we're talking about a specific moment in time, so "he did not use to understand me" is not a good follow-up. It should be "he wasn't understanding me" or even "he didn't understand me".
I believe this is one of the hardest sentences to translate from Portuguese to English I've seen in Duolingo. Given that "used to" does not fit here, "understand" is a stative verb so we can't use it in gerund and using past simple to both verbs does not deliver the idea intended by the sentence in Portuguese, I think that adding an idea of continuation to the sentence is the best possibility (though not exact at all), e.g. "I spoke in Portuguese, but he continued not to understand me". What do you guys think?