In the sentence, "bu4" means I don't want to do something. "mei2 you3" means I don't do something. For example. "wo3 bu4 chuan1 zhe4 tiao2 qun2 zi" means I have options and I choose not to wear this skirt "wo3 mei2 you3 chuan1 zhe4 tiao2 qun2 zi" it just means I don't wear this skirt

1) Why. :- could be due to the difficulty of translating the multitude of English tenses. The C-E re-translation would result in; "ta1 jin1 tian1 mei2 you3 chuan1 qun2 zi" (She)(today)(not has)(wear)(skirt) == She has not worn a skirt today. See marke li for the usage of "bu4 chuan1 zhe4" 2) Is..precise translation? See above.