Hello Soup,
Thank you for your reply.

I see. I remember I once met with an Australian but I couldn't understand him at all except one word I caught, that is "container" which the guy pronounced it as "contarna". I felt very frustrated about my English at that time because I had thought my English listening was very very lousy at that time.

But I could understand the English of Americans or Britons basically.
I am not a Shanghainese though I live here.

My mother tongue is Southern Fujian dialect, which is same with Taiwanese.

Yet, I can't speak it very fluently now. Whenever I speak with my friends, I always subconsciously switch it to Mandarin.

I understood very limited Shanghainese if the local people speak very very slowly.
I am not a good decoder.