Learnt and learned are both used as the past participle and past tense of the verb to learn. Learned is the generally accepted spelling in the United States and Canada, while the rest of the English-speaking world seems to prefer learnt.
Keeping this in consideration, is I have learned correct?
Explanation: Past Simple tense (I learned) tells only about the fact that occured in the past, while Present Perfect tense (I have learned) indicates a connection between the fact in the past and the present situation.
Similarly, why do British people say learnt?
Learnt is used for the past tense form and past participle of the verb to learn by speakers of British English. British English speakers will say learnt when referring to some sort of knowledge or information that they learned in the past. Thus, you would say, She learnt to play hockey at boarding school in Sussex.