Yes. This seems to work even when you pass it Chinese while maintaining ja-JP as the language

  function tokenizeJA(text) {
    var it = Intl.v8BreakIterator(['ja-JP'], {type:'word'})
    it.adoptText(text)
    var words = []
  
    var cur = 0, prev = 0
  
    while (cur < text.length) {
      prev = cur
      cur = it.next()
      words.push(text.substring(prev, cur))
    }
  
    return words
  
  }

  console.log(tokenizeJA("今天要去哪裡?"))

still seems to parse just fine. so most likely just using the passed input to parse.