Is Shanghai dialect regular?

Yes, and it's more complicated than Mandarin.

See:/Romanization

Let me give you an example. Mandarin has two stops, such as p-b, t-d and k-g (Ziqing-Quanqing).

Shanghai dialect is divided into three parts: p-b-bh, t-d-dh and k-g-gh (sub-clear-clear-full-voiced).

Shanghai dialect is a dialect of Wu dialect, and Putonghua can be said to be a dialect of Mandarin.

According to the definition of linguistics, Wu dialect and Mandarin are very different (both belong to the Chinese language family), and they cannot communicate with each other. It's not as simple as pronouncing a flat tongue.

Lexical grammar is also very different:

For example, how long does it take to say "how much time" in Mandarin and "how much time in Guang Chen" in Shanghainese?

Mandarin asks "Where is it?" Shanghai asked, "What are you going to do?" Lerak Gatek

There are survivors in Shanghai dialect who don't have Mandarin (such as "Yimen Li Laixu", Yimen Kaoli Likhe) and so on.