My question is: if this is true, why the heck is the pronunciation for standard Mandarin so different from the standard Beijing and northern accents? Seriously, especially with all the "er"s at the end of various characters. It does not sound similar to what is taught in standard Mandarin classes, and I speak as one who learned standard Mandarin for a number of years (in Canada and in China) and also lived in Beijing for a bit. I'd really like this explained to me, because the ear test tells me this is not true. But again, I've heard it said so many times that I am willing to consider it's possible.
https://en.wikipedia.org/wiki/E_language
It appears to be a Tai Chinese creole or mixed language (like a creole but without the massive simplification in grammar).
Yi(Loloish) is definitely a different language family though that wouldn’t stop people writing in Mandarin if they really wanted to. Vietnamese, Korean and Japanese were all written as if they were Classical Chinese to greater or lesser extents until relatively recently.
https://en.wikipedia.org/wiki/Loloish_languages
I’ve heard Sichuanese described as Mandarin without tones. All of Sìchuān speaks different forms of Mandarin for the same reason Manchurians do, recent massive resettlement, though not as recent as in 东北.
If Sichuanese sounds similar to Mandarin due to migration, it would certainly explain a lot. Thanks for that bit of information. But I would say that the differences between Sichuanese and standard Mandarin would be more from pronunciation differences than tonal differences.
https://en.wikipedia.org/wiki/Nuosu_language
> Nuosu is one of several often mutually unintelligible varieties known as Yi, Lolo, Moso, or Noso; the six Yi languages recognized by the Chinese government hold only 25% to 50% of their vocabulary in common. They share a common traditional writing system, though this is used for shamanism rather than daily accounting.
I bow to your superior expertise when it comes to the differences between Sichuanese and Mandarin but all of Sìchuān is definitely part of the Mandarin speaking area.
The book to buy if you’re interested in this is the Language Atlas of China.
Traditional and Simplified Charcters are only barely relevant to this. The only spoken varieties of Chinese with vernacular literatures are Mandarin and Cantonese. All writing in Chinese is in one or the other. Even in Hong Kong and Macau the overwhelming majority of writing is in Mandarin. It follows Mandarin grammar and vocabulary and can be read without any special difficulty by Mandarin monoglots. Written Cantonese is basically unintelligible to them. It’s used for songs, occasionally subtitling, a very small corpus of fiction and dialogue in court transcripts and scripts. This is orthogonal to the use of Traditional or Simplified characters. You can write any of the dialects of Serbo-Croatian in Latin or Cyrillic characters. That doesn’t make any of them Russian, or German.