Translation:My mother is eating a banana and a cherry.
I put: banana and cherry. No good.
It is either: banana and cherry.
or: a banana and a cherry.
maybe: bananas and cherries.
or: a banana and cherries.
but: a banana and cherry does not work unless it adjectival, in which case it presumably needs a noun.
I don't know Navaho, but I do know English...