When you translate a message from symbols or code into language, you decode it. British code breakers worked during World War II to decode Germany's coded messages.
You might need to decode a secret message sent by a spy, but some computer scientists also decode the symbols in computer languages into grammatically correct language. Sometimes older people don't understand the lingo that younger people are using — they might ask a grandchild to help them decode lines in a song, for example. When sound engineers translate between analog and digital signals, they also decode.