Then you transcribe and analyse it. Each year, we do this in our linguistics department. We take our students to Hong Kong or Okinawa or Malaysia to do field-work. You have about 5000 languages spoken in the world in some 125 nations. Simple arithmatic tells us that all nations are likely to be multilingual.
Japan is a very multilingual place.
Some languages like Nivkh in Wakkanai or English in the Ogasawaras or the Sanka dialects of Nagano have died out. However, in the north more people are learning and speaking Ainu than even 50 years ago. In the south, there are dialects of Ryukyuan. Korean is an urban-based language like Chinese which is spoken in the port areas of Yokohama and Kobe and Nagasaki. With many foreign workers in Japan now you can hear Philippine languages, Brazilian Portuguese and so on.