How to install styles and language packs?

[KernicDE]

See title. I added the volumes in docker-compose.yml, but when I start the container then, docker-compose shows some errors, that language files can't be found.

    volumes:
      - ./phpbb-sqlite:/phpbb/sqlite
      - ./phpbb-files:/phpbb/www/files
      - ./phpbb-store:/phpbb/www/store
      - ./phpbb-avatars:/phpbb/www/images/avatars/upload
      - ./styles:/phpbb/www/styles
      - ./language:/phpbb/www/language
      - ./ext:/phpbb/www/ext