So in German the number “21” is spelled “einundzwanzig” which means “one and twenty” compared to “twenty (and) one” in English. If you were to say “einundzwanzig” to me I’d most likely write down the 1 immediately and then put the 2 in front of it, if it’s utmost important to get the number right. This is really common also among the Dutch (they have the same thing) as well.
And one of our most common mistakes when speaking English is saying the number wrong. For example, 85 is pronounced fünfundachtzig, five and eighty, but it would not be uncommon for a German to misspeak in English and say fifty-eight.
I wonder if this has anything to do with what you wrote?
Could be inherited from arabic as cited by another (does all western numbering system derive from hindu-arabic?). What really intrigues me is why specially the tens are reversed. If it were some practical utility or reliability feature (saying the most important first/last?) I'd expect a fixed order throughout. Maybe it's just a random irregularity.
And one of our most common mistakes when speaking English is saying the number wrong. For example, 85 is pronounced fünfundachtzig, five and eighty, but it would not be uncommon for a German to misspeak in English and say fifty-eight.
I wonder if this has anything to do with what you wrote?