QUOTE
Dutch does, too.
No it doesn’t.
QUOTE
Danish and Swedish both change it.
Course they do. Otherwise they couldn’t say „the euro“
QUOTE
Finnish changes all forms
They have to, because a partitive is required after a cardinal number (greater than one)
QUOTE
this is natural to the languge which doesn't change many nouns in the plural case
This is true but has less to do with „many nouns“ than with units in general. Currencies don’t change anyway. It was always „zwei Mark“ whereas it has never been *“two pound“.
QUOTE
based in Old English since they were neuter nouns of the 'a' declension with a long vowel or diphthong which had identical singular and plural nominative and accusative forms
True: I sense some googling here
QUOTE
Not adding -s to English plurals is linguistically incorrect.
But this is still a generalisation to which I cannot subscribe, at least not in the way you formulate it.
The productive plural form (i.e. the way that plurals of words new to the language are formed) is with the „-s“ ending
QUOTE
The rules of our language's roots in Norse, Old Germanic, Latin and French demand the -s ending
Nope. Now you’re fishing about and have stopped googling.
Latin accusative plurals of the more common declensions did indeed use an –s.
(Old) Norse? No. If you want to generalise here then use an –r.
French? They may write an „s“ but do they pronounce it?
And how can these roots demand the -s ending nowadays?