2. The system according to claim 1 , wherein the server further comprises a second speech recognition device that receives a second utterance speech of the second language from the second speech input device, and recognizes the second utterance speech; a second machine translation device that consecutively translates the second language of the recognition result into the first language without waiting completion of the second utterance speech; a second speech synthesis device that generates a first speech of the translation result; and a second output adjustment device that outputs the second utterance speech and the first speech to the first speech output device by adjusting a volume of the second utterance speech to be smaller than a volume of the first speech.
2. The system according to claim 1 , wherein the server further comprises a second speech recognition device that receives a second utterance speech of the second language from the second speech input device, and recognizes the second utterance speech; a second machine translation device that consecutively translates the second language of the recognition result into the first language without waiting completion of the second utterance speech; a second speech synthesis device that generates a first speech of the translation result; and a second output adjustment device that outputs the second utterance speech and the first speech to the first speech output device by adjusting a volume of the second utterance speech to be smaller than a volume of the first speech. 5. The system according to claim 2 , wherein, when completion of the second utterance speech is detected, the first output adjustment device adjusts the volume of the first speech to be larger than the volume of the second utterance speech being outputted from the first speech output device.