why can a wizard cast spells in heavy armor that they have gained through multi-classign and whatnot and a barbarian cannot rage in the same?
— Shambridge Cramalinica (@FractallyWeird) June 26, 2018
A spellcaster of any sort can cast spells in armor with which they're proficient. That's a general rule for all spellcasting.
— Jeremy Crawford (@JeremyECrawford) June 26, 2018