Learnt = Much more common in British English than in American English
Learned = Used in both British English and American English
We learnt/learned of President’s death on BBC radio.
Jill learnt/learned the table of 11 by heart.
Though she was driven to distraction by the noisy niblings, she learnt/learned the speech in a few hours.
She learnt/learned Spanish from her mother.
She hasn’t learnt/learned her lines for the play yet while Maria played the scene with great skill.
She learnt/learned modesty from her mother.
He hadn’t given a damn about my advice, so I guess he learnt/learned the hard way.
There are a number of other irregular verbs like burnt/burned, leaped/leapt, dreamt/dreamed, spilled/spilt, knelt /kneeled, spoilt/spoiled, spelt/spelled, etc., which follow the same pattern in their past tense and past participle structure.
Note: It is learned (not learnt), an adjective which is pronounced as two syllables (lərn|əd) rather than the one syllable verb (ləːnt or ləːnd) means ‘having or showing profound knowledge’.
He is a learned and respected jurist.
The judge couldn’t dismiss the report as it came in an extremely learned journal.