> I don't know any other language where flexible argument order would work so well.

Any highly inflected language has such a property. Slavic languages, Sanskrit (or, more broadly, Indo-Aryan languages) are prime examples.

Speakers of Finnish and Hungarian will likely chime in and state something similar.

Finnish case markers vary a lot from word to word, because of not only vowel harmony but other features of the word stem, and consonant gradation which is a weird feature of Uralic languages.

For the subtraction example, some numbers would be 50:tä 5:llä and others 6:tta 3:lla. Of course you could encode for all those possibilities and successfully parse them, but it would feel weird for a compiler to reject an expression because it's ungrammatical Finnish.

Also it would feel weird if you first write (vähennä muuttujaa 256:lla) but then realise you made an off-by-1 and have to change it to (vähennä muuttujaa 255:lla) but that doesn't compile because it should be 255:llä, so you have to remember to change two things.

But on the other hand, that's just how it is to write in Finnish, so in prose we don't really think about it. In natural language, it's normal to have to change other stuff in a sentence for it to continue making sense when you change one thing.