No, it's not quite right. I'm learning English, but I still cannot speak it well.

no,should be"i am learning english,but i still can't speak it well"

Neal is right. "I'm learning English, but I still can not speak it well" is correct.

in oral English,it's okay to say so

Your sentence is not so right!!! Let me help you to correct it : I lern English, but still can not speak well (ㄨ) =I am learning English , but I still can not speak it(English) well (o) (This is present tense) If you dont learn English anymore you can say : I have learned English before, but I still can not speak it(English)well (This is past tense)