When and why did the number reading order change [duplicate]

Solution 1:

This is a very interesting question, but also a very complicated one.
It seems that the Jains, the believers in the old Indian religion Jainism, have invented the positional numeration ( at least they seem to have written the oldest known texts on the subject). Positional numeration means describing all integers with just ten digits whose value varies according to their position in the written representation and, of course, this necessitates the use of a zero digit which has no intrinsic value but functions as a placeholder.
The information relevant to the question is that they enunciated numbers by starting with the digit for units, then that for dozens, etc. In other words, the order opposite to the one used in contemporary English.

This does not answer the OP's question, but at least, since there have been deviations, we know from what they were deviations. I'm adding a link to a text (in French, unfortunately) by a historian who, interestingly for the users of this site, also evokes the Indian grammarian Panini. The point most relevant to our discussion is on page 199.