A code is a system of rules to convert information—such as a letter, word, sound, image, or gesture—into another form or representation. This can involve rearrangement, or replacement, or both. But, let’s look at some other terms;
Strictly speaking, a cipher is a method of encryption or decryption. Most often, this almost always involves replacement, but occasionally includes rearrangement.
A language game (also called secret language or ludling or argot) is a system of manipulating spoken words to render them incomprehensible to the untrained ear.
Language games differ greatly from ciphers in that they rarely involve replacement and rely solely on rearrangement. A language game such as Pig Latin or Spoonerisms may be used to conceal a message (spoken or written) but do not involve replacing any of the text or sounds rather simply rearranging them in a easily predictable and wholly parsable ways.
There are simpler ciphers, such as the Caesar cipher, and – it could be argued – this is a rearrangement rather than strict encryption. However, it stands to reason that a one-to-one cipher, such as the Caesar cipher still requires a key to understand, whereas Pig Latin only requires a basic understanding that the initial consonant has been moved to the end of a word and followed by “ay”.
It should also be pointed out that language games are just that, a fun or novel way to speak or write a language, but a cipher is rarely something that can be spoken and would likely sound worse than any language game changes that have been used to date.
Simply stated, language games, while an alteration of a language, are not replacements meant to encrypt communication. Ciphers, while an alteration of language, are not simple rearrangements of language meant to be spoken or easily parsed.