I can’t imagine it would be too hard to check the language choices of the previous episode watched and attempt to match them.
Biggest frustration with Plex viewing among my users is having to change subtitle and audio languages for every episode, especially for foreign TV shows and anime.
It becomes a pretty significant issue when viewing on a less input capable device, like a smart TV. Having to navigate through the menu for every single episode to change them makes Plex frustrating enough to not use if there’s any other viewing option out there.
There’s an existing feature suggestion thread discussing an option to select audio/subtitle for an episode based on the previously played one. I suggest you comment/vote in that thread in order to help us avoid distracting or cannibalizing votes.
Unless I’m missing some unique aspect I’ll therefore close this thread as a duplicate.