Mentalese

The concept of a proposition as something that can be expressed by sentences in both Mentalese and, say, English is an analogical extension of the concept of a proposition as something that can be expressed by sentences in both English and German.

Source: wiktionary

Translationists are said to treat the coding of thoughts in ‘Mentalese’, whose structure is already known, into a natural language, just like translating a natural language, say Russian, in terms of another known language, say English (G 282). Incorporationists point out the circularity of (36b) because Mentalese, supposed to be intrinsically intelligible, is just English or some other variety of a natural language, and the translation maneuver only postpones the problem, [...]

Source: wiktionary

But where does mentalese come from? If it is learned, then what is it related to in the preceding mentaleses? To avoid endless regress, [Jerry] Fodor postulates an internal language that is innate, a claim that he himself calls "horrendous" and "scandalous," yet inescapable.

Source: wiktionary

[A]re natural languages merely vehicles for the communication of mentalese? Or does language itself play a role in the formation of our thought? The question is called critical, since a positive response to the latter (language does play a role) would call into question the assumption that all meaning is reducible to mentalese.

Source: wiktionary