I've been reading up on non-sedentary peoples as of late due to the quarantine, and I came across a great deal of migrations during the 18-19th centuries. Either due to an escalation in warfare, or great power intervention/resettlement/genocide, most groups seem to have been laid low. But then I got to the Dungan Revolt.
While most of these events are understandably intense on the affected populations, the Wikipedia article for this cites a 20 million population decrease. So when taking about this and other events in China like Taiping, the numbers just seem absolutely incredible. The related events in China right now also bring extra attention to the question.
So would Qing China in 1850 have as diverse a linguistic population as Europe for instance? Or would it be largely the same region as we know today, just with a bit more color around the edges?
I don’t really want to try to speak about “sinicization” and I tend to shy away from terms such as these since cultures tend to adapt and choose what parts of other cultures they want to adopt. I think u/enclavedmicrostate can elaborate more on this in regards to the Qing Dynasty specifically. However, I do want to talk a little about the diversity of China in general.
Westerners tend to think of China and Chinese people as a monolithic people and culture, and to be fair, the modern mainland Chinese government tends to try to promote this image as well, and has done so pretty much since it came into power. Still, this is also certainly an aspect of colonial thinking on the part of Westerners. In any case, the truth is that, despite Wikipedia saying China is 92% Han Chinese or whatever, Han Chinese people themselves are really probably more culturally and linguistically diverse than all of Europe. The concept of a Han ethnicity really gained traction towards the end of the Qing Dynasty as a reactionary movement to Manchu rule, but this was and is pure politics. In terms of religious and cultural practices, philosophies, and especially languages, the “Han people” are extremely diverse. In fact, China is undoubtedly one of the most linguistically diverse countries of the world, Han people speaking hundreds of different “Chinese languages”. It’s not just language though. In terms of cultural practices, actually very little unites Han people culturally across the whole of China and Taiwan, and their diasporas. I talked about these few things in a comment a while back, which I will link here . Anyways, if you would like further reading on these topics, I would recommend the works of Melissa Brown, an anthropologist specializing in Chinese culture and especially Taiwan. A good example of her work would be Is Taiwan Chinese?. Highly recommended, if you want to understand how modern ideas of “Chineseness” have been cultivated politically.
Much as I wish I could go off and write an original answer, it wouldn't be very good given the limits of my knowledge of historical linguistics. The same is not true of /u/keyilan, who has written several answers on China's linguistic diversity, links to which can be found here.