I have been told that standard notation is virtually universal nowadays. Standard notation is, in my experience, read from left to right, a convention that came naturally to me because the only language I know how to read is read LTR.
Because all of the common markings are in Western languages that are also read LTR, this reading order makes sense.
Those who do not read a Latin-based language often do not read LTR (and sometimes not even RTL, either) or have any way of interpreting the written markings by finding similarities between their language and the language the markings are in.
Do people who speak/read languages like Arabic and Chinese write musical markings in their own language and/or read/write music no-LTR?
(Puzzle canons that are meant to be read both forwards and backwards, etc are not the focus of this question)