Qual a diferença entre "Learnt" e "Learned"

These are alternative forms of the past tense and past participle of the verb learn.

Learnt is more common in British English, and learned in American English. There are a number of verbs of this type (burn, dream, kneel, lean, leap, spell, spill, spoil etc.).

They are all irregular verbs, and this is a part of their irregularity.