Chinese languages

i am a native

I live in Shanghai. As i know, many Shanghailander(native wu dialect speaker) cannot speak Mandarin well(with accent ).Of course , they can understand it well. Actually , wu dialect is another language if you mean languages are classified by their pronunciation. So is Cantonese.

Chinatown=唐人街tang2ren2jie1
Chicago=芝加哥zhi1jia1ge1

I've already eaten = wo3 chi1 guo4 fan4 le

"verb + guo4 + le at the end of the sentece" means you have done something. But in real life , this can be complicated.