It would be really nice to be able to set voice-over and UI languages, separately, like AoE2:DE.
Selecting a language in AoE:DE makes it so both audio and text get applied simultaneously, unlike the sequel, which only affects text.
It would be cool if they were split up, so that we can pick audio and text language independently, and further customize our gaming experiences.
I’d like this very much. Normally, I like to watch movies in their original languages, while having subtitles and other text in my preferred language. If it was possible to change the UI language independently, that would be amazing.
Hopefully this is possible some day 
On Netflix captions don’t always match the translated language so what would you do in that case?
Not sure if I understand your question. But if you mean those words in certain languages that are unknown and don’t have active subtitles, well… that is in fact an issue. But that problem wouldn’t be part of this game since it does not include texts other than what is shown within the strings.txt file.
I meant captions not matching translated audio.
Oh! I understand. Yeah. That does not happen in English, right? I know bot AoE1:DE and AoE2:DE have this issue for different languages other than English, and I hate it. I managed to make the texts consistent with what is said in Spanish (MX), by editing the strings.txt file. It was tiresome, but eventually, everything (?) got synced with the audio 
I still have hopes for this to be a thing. To be able to listen to the original voice over while enabling other language for written text is pretty nice in AOE2:DE.