Language games are games that manipulate an already existing language to create a sort of secret language.

For example, adding "y" after every two letters in English: Hello, my name is Bob. --> Heyllyo, myy ny amye iys Byoby.

Language games are usually played by younger children. They can even have their own dialects, depending on where they are spoken. For example, in Pig Latin, "yay," "way," and "bay" are used, depending on where the kids are that are speaking it (for the record, I spoke with "way").

You could technically consider these ciphers.