Add Language and Country Refine Options for Lists

You could keep just 1 list and use Advanced Title Search to split the contents:
https://www.imdb.com/search/title/?languages=en&lists=ls060663034
versus
https://www.imdb.com/search/title/?languages=!en&lists=ls060663034
(where the ! was inserted in the url manually to indicate I wanted no English titles).

HOWEVER, the problem is, languages are attached to films when there is just a little in the film. The first entry in the English list is The Wages of Fear (1953), which is a French film (and I don't remember any English dialog, signs, etc., but it's been a while since I watched it.)
In fact, there are 10 films on that list which have both English and French designations (and now I'm seeing British films where I don't remember French.)
https://www.imdb.com/search/title/?languages=en,fr&lists=ls060663034

So instead let's use the Country designation.
On that particular list, that looks much cleaner:
https://www.imdb.com/search/title/?countries=fr&lists=ls060663034
But in the modern era, with many production companies and funding sources, that gets complicated.

For instance, this film
https://www.imdb.com/title/tt6428150/?ref_=nv_sr_1?ref_=nv_sr_1
seems very American when you watch it. But it will come up on a search of Romanian films too, because it was partially filmed/financed there.

So really, your separate lists of films by how YOU feel each film should be classified are really best for you.

Thank you for your insight (and sorry for the slow reply!).

That makes sense. I had a feeling such overlaps could pose a problem, which isn't necessarily IMDB's fault. Still, ideally, there would be a way to filter by original language, as I always prefer to listen to them with subtitles. Until then, I will likely take your suggestion. In the end, it's not a big deal anyway.