code: def get_browser_locale(self, default: str = "en_US") -> tornado.locale.Locale:
          
          if "Accept-Language" in self.request.headers:
              languages = self.request.headers["Accept-Language"].split(",")
              locales = []
              for language in languages:
                  parts = language.strip().split(";")
                  if len(parts) > 1 and parts[1].startswith("q="):
                      try:
                          score = float(parts[1][2:])
                      except (ValueError, TypeError):
                          score = 0.0
                  else:
                      score = 1.0
                  locales.append((parts[0], score))
              if locales:
                  locales.sort(key=lambda pair: pair[1], reverse=True)
                  codes = [l[0] for l in locales]
                  return locale.get(*codes)
          return locale.get(default)
docs: Determines the user's locale from ``Accept-Language`` header.
  
          See http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.4