Velta Ruke-Dravina's "The Standardization Process in Latvian" analyzes the language of these early texts, I suggest you check there.

There doesn’t seem to be much of a consensus about the location of an Austroasiatic homeland, or about other issues of historical reconstruction for this family, but George Van Driem’s 2006 article in the M-K Studies Journal can provide some background.

@user6726 Good point! I don’t know how similar the gender systems of Khasi and the Munda languages are, and the other languages in its branch, Khasi-Khmuic, don’t have gender. It’s conceivable that Khasi had gender at some early stage of the language, lost it at the time that Khasi-Khmuic was one language, then innovated it anew in the way I’ve suggested.

That source is a general work on ethnicity based on 2nd or 3rd hand knowledge, so not credible on this point. Unfortunately Wikipedia has picked up this piece of misinformation.

Sorry to sound condescending, but the Vietnamese heartland was part of China proper for over a millennium. That accounts for the influence of Chinese culture there, including the use of Chinese writing. The situation was very different in the rest of SE Asia, including Thailand. Can you point to one text written in Thai using Chinese characters, either before the invention of Thai writing in the 13th century or at any other time? They don’t exist.

Thai never used Chinese characters, where did you get that idea? Vietnamese is an outlier w/i SE Asia as far as Chinese influence goes - this is a basic fact about SE Asian history.