I'm getting my data from geofabrik.de, render them using tilemaker, then I serve them using tileserver-gl and it by default uses maplibre. My styles are the default/example styles that tileserver uses in its example here, which are osm-bright and klokantech-basic.
I did this procedure for data of Iran (Perso-Arabic script), Iraq (Arabic script), and U.S. (English/Latin script). NO LABELS on map of Iran and Iraq, but HAS LABELS on map of the U.S.
The problem was with Glyphs and this solved my issue:
https://rastikerdar.github.io/vazirmatn/fa
https://github.com/openmaptiles/fonts
or a docker if it's hard to set up.