[akalsz]

I believe that these conventions (at least for dates) are indeed the most practical for their respective languages.

Take for example "October the third, two thousand nine" (10/3/2009, MDY). In German one would pronounce this as "der dritte Oktober zweitausendneun" (3.10.2009, DMY). In Hungarian "kétezer-kilenc október harmadika" (2009. 10. 03., YMD). All of these pronunciations reflect the order numerical dates are written: using any other convention would simply make them less natural to pronounce.

Now it is certainly not unheard of that the order of pronunciation also changes (see the British "the third of October"), but changing language is a lot harder ­ in some cases impossible without breaking grammar ­ than changing written numerical representations.

[saithound]

Certain orders are grammatically more convenient in certain languages, but that's not the same sense of practical as the one referenced above: cf. "inches are more practical than meters because they have the same spelling in American and British English", vs. "inches are more practical than meters because they're human-scale units".

Sure, date order may be decided based on accidental grammatical features of the target language. But that just reaffirms that "practicality for the common man" is rationalization.

Naturally, the written convention need not affect pronunciation: in the case of numbers, the world standardized on decimals with place values increasing from right to left, but most languages retain their own idiosyncratic ways of naming/reading them This causes negligible friction in practice.