I would counter-argue that numbers are part of the language.
If you prefer reading from right-to-left but your country reads it from left-to-right, should choosing what reading dicrtion be an option?
What about choosing colour or colour should that be a user preference too? What if one’s country spells Japan as 日本国 but prefer to spell it as 日本國, should kanji variants be tied to a locale or be a user prefrence?
What about choosing long vs short scale numbers, should that be a user preference too?
Date formats?
Using dots in language that only uses comma as a decimal separator wouldn’t be correct and I don’t think should be displayed it that way if it isn’t considered correct even if one user don’t prefer it.
Even if a language has multiple notation preferences it’s usually by region so you could change the territory part.
I’ve clearly outlined a use case above where I am a non-English user of which the locale would normally give me comma-delimited decimals, but I want dot-delimited decimals.
If Roblox starts forcing me the wrong notation, I don’t want to have to figure out what locale I need to undo it. It should be a separate preference for UX reasons.
Numbers aren’t language, and dates aren’t language either. Both number and date formats should be preferences (with sensible defaults). The language-specific differences are part of the language, number/date formats are not as tied to the language.