Learnt and learned are not the same thing at all.

Learnt is the past tense of the verb to learn and is used in the simple past (preterite). I learnt French at school.

Learned is the past participle and used in the perfect tense. I have learned to speak French.

A verb which behaves in a similar way is dream.

Last night dreamt I was in an aeroplane.

I have often dreamed of winning the lottery.

However, as most native English speakers don't know the difference and the tendency is to standardize or use either form I wouldn't bother about which form you use; however strictly, the above is correct.