https://bugzilla.redhat.com/show_bug.cgi?id=2262410
--- Comment #6 from Akira TAGOH tagoh@redhat.com --- That is weird. Noto Sans Arabic doesn't have "en" covarage. I can't reproduce this except running with --osd-font="Noto Sans Arabic". Do you have any your own config? how can I reproduce this? I tried `LANG=en_US.UTF-8 mpv --player-operation-mode=pseudo-gui filename-mixing-12345.mp4` but it works as expected. but `LANG=en_US.UTF-8 mpv --player-operation-mode=pseudo-gui --osd-font="Noto Sans Arabic" filename-mixing-12345.mp4` not.
FWIW Noto Sans Arabic doesn't have alphabet glyphs. apparently libass is falling back to reuder alphabets. though Noto Sans and Noto Sans Arabic has same outline for numeric characters. If mpv use Noto Sans as a fallback, the rendering should be like your screenshot. I suspect something may went wrong in libass.