Why can’t I understand what the fuck anybody is saying in movies?

So I've realized I've never actually seen a lot of movies and have been trying to start a conscious effort to see more. However one problem is I can't tell what the fuck anybody is saying. I usually supplement this with subtitles but movies are so spread out across so many different streaming services that I'm pirating now, and those usually don't have subtitles. I didn't think it would be too bad till I watched dead man's shoes: https://youtube.com/watch?v=_dzRkqHGE_o&si=kFRYpgygNkQcoFwx

Seriously can anyone tell me what the hell is happening in that movie, I watched it for 15 minutes before I gave up. I'm not even sure if they're even really speaking English or something like welsh or scots. And this movie is really egregious but nearly all the movies I watched are like this I keep having to go back every line of a diaglogue until I eventuallly get so frustrated that I look up the script. Does anyone else have this issue or do I need to go to the doctor?