Bit of an old thread but interesting question.
In the case of Brainfuck you can sort of deduce which type of cipher was used by analyzing the ciphertext. For example: you’ll notice that a certain (plain text) string will have a different substitution for the same character. So “Hello world” might become “Jzbnu rpndm” (not really, just an example)
See how the first occurrence of the character ‘o’ is different from the second occurrence? If you do some google you’ll find that this is called a Polyalphabetic Cipher. The best known polyalphabetic cipher is the Vigenère cipher so it would make sense to start with that one.