It didn't accept HE GETS DIRTY. I reported it since it means the same as BECOMES.
I wrote "he is becoming dirty" and was rejected. Makes no sense to me. I reported it.
That is exactly what happened to me just minutes ago as of the time of this post. I reported it, and the results are still pending.
Feb 18, 2020 The present progressive is still not accepted.
He is becoming ( or getting) dirty was NOT wrong
"He is getting dirty" was accepted.
"He will get dirty" not accepted.
The German sentence is present tense "He is getting dirty." The future tense would need an extra "werden"-- one for the future "will" and one for the main verb "become/get," so that would be "Er wird schmutzig werden."
Just curious, is duo lingo going to expand their Latin and Hawaiian lessons?