You are right. This assumes Mandarin. Given the constraints and so many compromises I've taken, this isn't too bad a stretch. After all, all other dialects in Mainland China are seldom used in written text, especially in the field of technology. Mandarin is the one and only go-to option. I am not judging whether this is good or not, but it is the current situation of Chinese languages.

Kind of like Japanese where dialects can be different enough to be mutually incompatible but are all written using Japanese, and the national dialect/lingua franca is "Hyoujun-go" (literally "Standard Language") based almost entirely off of the Tokyo dialect which itself is a subset of the Kanto dialect.

Written Chinese is usually mandarin.

Chinese is a phonetic language. If you want to write in Shanghainese (as in the language as part of the wu family) your choice of characters for even common word would be different than if you write in Mandarin Chinese.

https://en.m.wikipedia.org/wiki/Shanghainese