Why are English verbs so different? 1)why do some people say "I have GOTTEN" instead of saying "I have got"? 2) the verb to learn. I hear 2 phorms in past tense: I learnd vs I learnt. Why does it have 2 phorms? Maybe there are many such examples in English. Please tell me about them.

Can anyone explain describing past tens in Chinese? What is the difference between 了 and 过？