With etymological history tracing the roots of the word "language" back to the Middle English, Old French and Latin words for "tongue,"  the very nature of language is tied to ideas of communication and expression. The common thread in all of the varying definitions of language is the concept of rifts between individual people, animals, even inanimate objects and how those gaps may best be bridged. Inherent, however, in this idea of connection and communication is the separation that language may often imply by its very definition. Beyond the conflict in definition, the idea of language raises serious questions in regard to where it falls in terms of medium, media, and mediator.  The varying manifestations of language fit with different theories of media as demarcated by Peirce, McLuhan, Lacan, and Saussure.
In its most basic form, language is the primary mode of communication--the expression of thoughts, feelings, and ideas to another. Different subsets of language are defined by speech and vocal patterns, written systems, and the specialized vocabulary or phraseology required by particular professions, as well as non-verbal systems ranging from body language and kinesics to communication between animals to the modes and systems in which computers exchange data. One definition in the Oxford English Dictionary refers to language as "applied to methods of expressing the thoughts, feelings, wants, etc. otherwise than by words." Under this category may fall dance, facial expression, and other commonly accepted conditions [see movement, face]. One example of non-verbal communication worth considering is the cinema of the silent era [see film]. Often, a dye wash would be employed to add visual interest to the black and white film stock used at the time. Each color came to take on a specific meaning that would not change from film to film: blue came to mean night, red danger, pink dawn, etc. Additionally, a stylized gesture system came to take the place of spoken words, allowing emotions to be understood without speech and only a periodic use of titles.  Language systems of this definition may be comprised of any socially understood practice: flowers may take on specific meanings,  the movements of a lady's fan held a particular meaning in Regency England, colors, movements, as well as what one may consider unarticulated sounds.
This definition of language aligns itself most clearly with the writings of Peirce. Peirce's theories of semiotics examines the divisions of words and communications into doctrines by which a sign or idea is communicated to an outside party. Each of the above mentioned methods of communication reflects to a varying degree what Peirce sees as the key to sign theory: making known an Abstraction (Peirce, 98). While utilizing diverse methods of embodying particular emotions and ideas, each of these subsets of language works toward what Peirce defines as being a sign: each "stands for something, its object" (Peirce, 99). The object may be an emotion, a state of mind, or an idea. The method of representation may vary from speech to movement to creating a unified system of color.
Conversely, however, language may create barriers as it strives to create open communication. The Oxford English Dictionary defines language first and foremost as "the whole body of words and of methods of combinations of words used by a nation, people, or race." Exclusion of others becomes inherent in this conception of language. As it bonds some together, language may separate others along the lines of nationality, class, and race. Speech patterns may reveal more about a person speaking than the words themselves. In Shakespearean texts, the speeches (and often, the dialogue) of noble-born characters are written in blank verse.  Lower born characters, by the class expectations of Elizabethan England, would (with notable exceptions) be uneducated, with comic relief found in their blatant malapropisms and grammatical blunders. Unlike the rhythmic lines of their social superiors, these characters speak in prose, often using contemporary slang and more vulgar sexual innuendos. In this instance, the very nature of their speech is a language in and of itself, speaking far more than their words about their birth and position in society.
By this definition, the role of language changes from a mediator of ideas between two parties, to approach Marshall McLuhan's definition of media. To McLuhan, "the media is the message" (McLuhan, 7). In this case, language has the ability to say more than the content of its words: the language itself is revealing. For McLuhan, media is never as isolated as one might think, and the very use of media itself becomes key to the content of what is being communicated. Out of this theory comes McLuhan's famous supposition that the message and the media are one, and neither can be separated from the other. Such is the case in this way of looking at language: the content and the mode of communication are braided--interlacing and inseparable, language here ceases to be a method to be utilized by a mediating power, becoming a media unto itself, using the mediator as much as the mediator may use language.
Moreover, when viewed in this light, the failures of language are brought to the fore in the discussion of expression. As a tool to express abstract ideas, Peirce describes semiotics as "eminently fallible" (Peirce, 98). While a sign may hold a specific connotation to the mediator, the same sign may have a very different meaning to the transmittee of any given message. When dealing with language, one deals with the removal by varying degrees of what one hears to the original thought. Before one may understand what another has to say, that other must find words for his thoughts, which must be understood (bringing up issues of word choice and connotation). The room for error is great, and grows with each step away from the original, abstract thoughts like a game of "telephone." 
The gaps in our ability to fully and truly express an Abstraction are unquestionable. These holes in language, however, are reminiscent of the failure of Lacan's "natural reality" (Lacan, 4) to be completely sufficient. Lacan describes the experience of a young child, learning about the world through empirical experience but still too young to possess the intellectual capabilities to truly understand what he sees. For Lacan, the moment this baby first sees (and recognizes) itself in a mirror, the pieces of himself that he has seen (arm, leg, hand, foot, torso) come together as a whole. The whole that he sees, however, is not really what he is--rather, it is a reflection. The mirror gives truth and hides reality in the same moment. Echoing the tendency of Lacan's mirror to render incomplete what it seems to make whole, language may divide where it seems to unite, leave questions when it seems to give answers. Just as the baby can never see its true self--only the reflection in the mirror  --language can never fully express one's abstract thought to another. Somewhere in the translation from idea to articulated thought to spoken or written word to what is understood by the audience, something will be lost.
Language presents a challenging conundrum to the student of media theory. Able to unite and divide at the same time, the greatest divine gift and the ultimate punishment, the very mythology of language manifests the duality of the definitions and contrasting ideas.  The transmission of a thought is almost as difficult to trace and describe as it is to successfully perform. In his Course in General Linguistics, Saussure puts forward the difficulty in ascribing words to represent objects and ideas. The relationship between the signified and the signifier is arbitrary. The meaning in the relationship comes from a learned association. For example, the word "tree" in and of itself does not resemble or call to mind the actual thing one would find in a forest. The reader knows the meaning because he has been taught over a lifetime that the tall brown and green plant one chops for wood and sits under for shade is "tree." For all intents and purposes, however, "tree" might just as easily be replaced with "zebra" or "Bob." This randomness in nomenclature raises an entirely new set of questions: if language is nothing more than a commonly accepted system of signs, an arbitrary relationship between signs and realities, communication is bound to be rife with confusion.
Beyond its compound definition, the variances that arise in concept make language distinctly hard to categorize. Language is unique in the sheer number of forms in which it may exist; language crosses the boundaries of visual (pictogram, hieroglyph, sign language, alphabetic writing, character languages) and aural (speech). As with many things that relate to media theory, it is hard to write a hard and fast rule for language to firmly place it under the category of "media" or "mediator." Christopher Nolan's 2001 film Memento drives home the point that even when one may feel in control, it is still possible that the power relations are not what they appear. 
Similar issues of a confused dynamic of who is controlling who is brought up in the 1999 Wachowski Brothers' film, The Matrix, making an interesting metaphor for the issues raised in the idea of language. As with the changing status of language as medium, media, and even mediator, The Matrix raises the question of what happens when roles are reversed, and what was thought of as the tool becomes the operator. The Matrix also brings the question of computer language to the fore. Computer code is commonly accepted as a language.  What are the implications of humanity being reduced to binary code? If such is the case, who is there left to decipher said code?
These questions, while unanswerable in many respects, shape our perception of the thoughts that surround media theory and the very words in which we are able to express and discuss these ideas. When the very tools we require to shape our thoughts and discussion must be debated, what effect will this debate have on the discussion itself? How can we speak of anything if we are unsure of the nature of our own words?