There was a recent question posted asking about how to interpret kaomoji, which promptly started garnering close-votes. Setting aside the question of whether that question is a good question or too general in scope, is off-topic really a valid reason for closing it?
Kaomoji, and similarly emoticons in English and other languages, aren't necessarily words you would find in an official dictionary. Then again, neither is most internet slang, but that still doesn't mean someone using slang isn't speaking a language.
a systematic means of communicating ideas or feelings by the use of conventionalized signs, sounds, gestures, or marks having understood meanings
Sure, something like (^^;) isn't your traditional hiragana symbol. Yet, on the internet, it still is a way of communicating an idea or feeling with a mark that is understood (in this case, the concept of 苦笑).
Moreover, the various symbols used in one language don't necessarily carry over to another language, which suggests some cultural or perhaps linguistic influence. For example, compare the common emoticons in English to the common kaomoji.
Aren't kaomoji as much a part of the Japanese language as other slang words?