This reminds me of when I used zeroeth, oneth, twoth, and threeth, instead of first, second, and third, for referring to indices 0, 1, 2, and 3 as a TA. It's less verbose than “at index zero”, but feels a little clumsy.
So the 'first' item in the list is actually the second?
The problem is you're trying to redefine English (and probably most other languages). The first item on a menu is, well the first item, like first place in a marathon, the first day of the month.
Surely a definition of the zeroth item would be something like an item that does not exist, the item that's left when you take away all the other items, etc.
Ordinals are 1-indexed. Language is 1-indexed; The #1 player is the best player, and so on.
zeroth is the ordinal associated with the cardinal zero.
For example christmas is the zeroth day after christmas.
A common advice with regards to user inputs is that if you do not do ordering or arithmetic on a piece of data (eg a phone numbers) then it should be a string even if it is numeric.
Similarly n-indexed conventions should be considered in terms of practical pros and cons.
Linguistic similarity is not a convincing argument to me.