Full Idea
Mentalese doesn't need Grice's theory of natural-language meaning, or indeed any theory of natural-language meaning whatsoever.
Gist of Idea
Mentalese doesn't require a theory of meaning
Source
Jerry A. Fodor (In a Critical Condition [2000], Ch. 6)
Book Reference
Fodor,Jerry A.: 'In Critical Condition' [MIT 2000], p.68
A Reaction
Presumably what is represented by mentalese is a quite separate question from whether there exists a mentalese that does some sort of representing. Sounds plausible.
Related Idea
Idea 2524 A language of thought doesn't explain content [Dennett]