"a possibility that was raised by some studies that found that in Arabic-speaking countries, where letters and numbers are read right to left, the mental number scale was reversed."

This is wrong, despite Arabic being an RTL language, in Arabic numbers are written, and read [1], in the same orientation as in Latin, Left to right. e.g. So 1,230 is written in the same orientation in arabic.

[1] this applies to all numbers with more than 3 digits. things are a little more complex for 2 digits numbers. As in English and French 12, or 11 are speller as "one word", however 35 in Arabic is spelled five and thirty instead of thirty five.

[2] the "latin" numerals are actually arabic numerals. The current numbers used in Arabic speaking countries are suspected to be of Roman origin according the wikipida article https://en.wikipedia.org/wiki/Arabic_numerals.