While tongue refers to the fleshy organ in the mouth used for taste, speech, and swallowing, language refers to a system of communication used by humans.
Here's the difference:
* Tongue is a physical part of the body.
* Language is a system of symbols and rules for communication.
Examples:
* "The child stuck out its tongue."
* "They spoke in a foreign language."
However, "tongue" can be used metaphorically to refer to a language, but it's not a direct synonym:
* "He speaks with a forked tongue" (meaning he's deceitful).
* "She's fluent in the tongue of Shakespeare" (meaning she speaks English well).