Also, note that we say “the blind” and “the deaf” referring to groups of people, not “the blinds” and “the deafs”. It’s a consistent pattern in English.
I thought this had already been explained, but perhaps not.
That’s an ordinary noun, not a nominative accusative. The way you know this is that you can say ‘an Untouchable’ just like you’d say ‘a car.’ You couldn’t say ‘a miserable’ because it’s a nominal adjective rather than a noun. ‘Miserable’ is an adjective being applied to a larger group, not a noun naming individuals within that group.
‘The Untouchable’ could be used as a nominal adjective, but it would then be referring to the whole group, not the individuals.
I also want to point out that conversion seems to happen more often in other languages, and, thus to translate we have to add the word “one” at the end.
The example that comes to mind is les petits, the little ones. There is no context I can think of where “the little” can be used as a noun in English.
They’re not nouns, they’re simply nominal adjectives that refer back to an earlier word. However. I speak very little French so don’t know if ‘les petits’ in French is a nominal adjective phrase or a noun phrase.
“Give me your tired, your poor,
Your huddled masses yearning to breathe free,
The wretched refuse of your teeming shore.
Send these, the homeless, tempest-tossed to me,
I lift my lamp beside the golden door!”
Hijacking this thread back to the OP, I would call such usage “substantive”. The opposite thing, using a noun as a modifier of another noun is called “attributive”. Attributive nouns are normally emphasized, while adjectives usually are not (save when you want to call attention to the them: “the red book” (and not the green one)).
Compare “French teacher” with “French teacher”. In the second, the teacher is French, an adjective used substantively and it means a teacher who is French. In the first, that same substantive adjective is used attributively and it means a teacher of French.