An artificial intelligence device includes a microphone configured to acquire speech including a plurality of languages, and a processor configured to generate, from the speech, text data corresponding to the speech, generate a plurality of pieces of separated data acquired by separating the text data for each language, perform natural language understanding processing corresponding to a language of each of the plurality of pieces of separated data to generate a natural language understanding processing result for each of the plurality of pieces of separated data, acquire command information about a command to be instructed by the speech and slot information about an entity subjected to the command, based on the natural language understanding processing result, perform an operation corresponding to the speech based on the command information and the slot information, and generate a response based on a result of performing the operation.