In bitcoin wallet that support bip39 mnemonic code, is there a way to get the 12/24 words from the seed generated by them? Or the translation is one-way only (from words to seed)?
There is no way to convert the resulting seed back to the original mnemonic.
As stated in the BIP 39 proposal:
To create a binary seed from the mnemonic, we use the PBKDF2 function with a mnemonic sentence (in UTF-8 NFKD) used as the password and the string "mnemonic" + passphrase (again in UTF-8 NFKD) used as the salt.
The seed (and optional passphrase) are passed through pbkdf2, which is not reversible.