Dative plural adjective and noun endings: den neuen Büchern vs. den neuen Autos?
I'm a bit confused. For dative plural, nouns end with n, the adjective ends in en, and the definite article is den.
So, for example: Der Junge lernt von DEN neuEN BücherN (the boy learns about the new books).
But, in the following example, the noun ends in s: Der Junge lernt von DEN neuEN AutoS (the boy learns about the new cars).
Why does das Auto end in S instead of N, as per the default rule? I'm assuming because das Auto ends with the "o" vowel, but I can't find any rules about this.
This happens with loan words and short words. Auto is short for Automobil which behaves like a German word.
And yes the s comes for plural with words ending with a vovel (or y), which don't exist in German for centuries.
The same happens with other languages like Italian or Russian where these recently imported words do not fit into the declination system.
There is also a trend in German not to try anymore to fit freshly imported words into the system.
This affects even words which formerly used the German way.
Taxi/e --> Taxen now nearly always Taxi --> Taxis
I take it like this:
das Buch (singular) | die Bücher (plural) | mit den Büchern (plural dative)
das Auto (singular) | die Autos (plural) | mit den Autos (plural dative)
... because what? if you wanted to add the "n" then it would be: MIT DEN AUTOSEN ??? brrrr, sounds horible
EDIT: I read your post again, the answer to your question is the S in AUTOS is there because it's plural, not because it's dative
Referring to your question I totally agree with gisberth: Abbreviations and words from other languages are at first (=for some centuries) declined by just using an -s in Genitiv (Singular) and in every case of Plural. Later the word can be included and get an own declension. Or it is forgotten or replaced by another word (often of original language) and disappears. Example for the first option: der Tunnel; Plural: former: die Tunnels, today: die Tunnel (English translation: the tunnel)
But I do not agree with your translation von-about:
"von" means usually "by" and I would understand your sentence "Der Junge lernt von den neuen Büchern." as "The boy learns by (using) the new books." "The boy learns about the new books." would be "Der Junge lernt über die neuen Bücher." "about" means "über"