This affects version 9.0.1. Regional variants seem to have missing lang when describing their form when you put your cursor over them. This seems to affect Alolan, Galarian, and Hisuian forms at least since I tested with Alolan Vulpix, Galarian Weezing, Hisuian Typhlosion, Hisuian Arcanine, and Hisuian Avalugg. This does not seem to affect Heat Rotom, though.
Here is a screenshot:https://imgur.com/a/Ix2AMew
How to reproduce:
1) Give yourself an Alolan Vulpix.
2) Open your inventory.
3) Bring your cursor over Vulpix.
4) Notice that the second line says "pixelmon.vulpix.form.alolan Form" instead of "alolan Form" or "Alolan Form"
Tested using The Pixelmon Modpack Beta on CurseForge, with no external JSONs enabled.