They pronounce "de" as de. I thought it's "dom".
I would be interested to know if the badly pronounced words have been reported to the TTS supplier. Duolingo is a challenging and high profile test for a TTS. One would think they would like to showcase their product at its finest. Surely the software will internally allow for some word by word tweaking (since languages are full of inconsistencies) so maybe it would not be a huge deal for them. Just my 2p.