Their shapes look like hieroglyphs on ancient tablets. It is said that the two are somehow related.
It draws symbols all over the place to mark its territory. In towns with many Smeargle, the walls are covered in graffiti.
- Regice, Registeel, Regirock, Regigigas, Regidrago, Regieleki (The dots on their faces don't seem to be Braille, although the puzzles to unlock them are.)
There are also a lot of Pokemon like Galarian Slowking, Phantump and Mismagius, who use curses/incantations. It's not mentioned whether or not they are speaking in English/Japanese, though. Other Pokemon like Ampharos, Beheeyem and Chinchou are explicitly stated to communicate with light.
I believe that's everything. If I missed one, please let me know.