Below is a definition of language that I found online. If you agree with the definition, would your comment about SEE CUED and PSE not being a language still hold true? If you don't agree with the definition please provide a source of your information.
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Main Entry: lan·guage
Pronunciation: 'la[ng]-gwij, -wij
Function: noun
Etymology: Middle English, from Anglo-French langage, from lange, langue tongue, language, from Latin lingua -- more at TONGUE
1 a : the words, their pronunciation, and the methods of combining them used and understood by a community b (1) : audible, articulate, meaningful sound as produced by the action of the vocal organs (2) : a systematic means of communicating ideas or feelings by the use of conventionalized signs, sounds, gestures, or marks having understood meanings (3) : the suggestion by objects, actions, or conditions of associated ideas or feelings <language in their very gesture -- Shakespeare> (4) : the means by which animals communicate (5) : a formal system of signs and symbols (as FORTRAN or a calculus in logic) including rules for the formation and transformation of admissible expressions (6) : MACHINE LANGUAGE 1
2 a : form or manner of verbal expression; specifically : STYLE b : the vocabulary and phraseology belonging to an art or a department of knowledge c : PROFANITY
3 : the study of language especially as a school subject
4 : specific words especially in a law or regulation <added language prohibiting further development along the river>
Source:
Merriam-Webster Online