changeHlQueryToJapanese.user.js

// ==UserScript==
// @name         Change hl Query To Japanese When Searching Japanese Letters
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  try to take over the world!
// @author       You
// @match        https://www.google.com/search*
// @icon         https://www.google.com/s2/favicons?sz=64&domain=google.com
// @grant        none
// ==/UserScript==

(function () {
  const JP_QUERY = { 'hl': 'ja' }

  const _test = () => {
    const assert = require('assert')
    const okList = ['宝', 'ナ', 'あ', 'ぬ', '県', '圏', 'ヰ', 'ゑ', '獄', '髙']
    for (let l of okList) {
      assert.equal(UnicodeUtils.isMaybeJapanese(UnicodeUtils.letterToUnicodes(l)), true);
    }
    const ngList = ['🐹', '한', 'A', 'a', '&']
    for (let l of ngList) {
      assert.equal(UnicodeUtils.isMaybeJapanese(UnicodeUtils.letterToUnicodes(l)), false);
    }
  }

  const UnicodeUtils = {
    letterToUnicodes: (letter) => {
      return Array.from(letter).map(v => v.codePointAt(0));
    },
    isExtraKanji: (unicodes) => {
      if (unicodes.length !== 1) { return false; }
      // https://ja.wikipedia.org/wiki/Unicode
      return 0x20000 <= unicodes[0] && unicodes[0] <= 0x3ffff;
    },
    isCJKKanji: (unicodes) => {
      if (unicodes.length !== 1) { return false; }
      // https://ja.wikipedia.org/wiki/CJK%E7%B5%B1%E5%90%88%E6%BC%A2%E5%AD%97
      return (
        (0x4e00 <= unicodes[0] && unicodes[0] <= 0x9fff) ||
        (0x3400 <= unicodes[0] && unicodes[0] <= 0x4dbf) ||
        (0x20000 <= unicodes[0] && unicodes[0] <= 0x2A6DF) ||
        (0x2A700 <= unicodes[0] && unicodes[0] <= 0x2B738) ||
        (0x2B740 <= unicodes[0] && unicodes[0] <= 0x2B81D) ||
        (0x2B820 <= unicodes[0] && unicodes[0] <= 0x2CEA1) ||
        (0x2CEB0 <= unicodes[0] && unicodes[0] <= 0x2EBE0) ||
        (0x30000 <= unicodes[0] && unicodes[0] <= 0x3134A) ||
        (0x31350 <= unicodes[0] && unicodes[0] <= 0x323AF)
      );
    },
    isKatakana: (unicodes) => {
      if (unicodes.length !== 1) { return false; }
      // https://ja.wikipedia.org/wiki/%E7%89%87%E4%BB%AE%E5%90%8D
      return (
        (0x30A0 <= unicodes[0] && unicodes[0] <= 0x30FF) ||
        (0x31F0 <= unicodes[0] && unicodes[0] <= 0x31FF) ||
        (0x1B164 <= unicodes[0] && unicodes[0] <= 0x1B167)
      );
    },
    isHiragana: (unicodes) => {
      if (unicodes.length !== 1) { return false; }
      // https://ja.wikipedia.org/wiki/%E5%B9%B3%E4%BB%AE%E5%90%8D
      return (
        (0x3041 <= unicodes[0] && unicodes[0] <= 0x309F) ||
        // これは仮名補助。ひらがななのかカタカナなのかよくわからないけど、今回の問題解決には無関係なので保留している。
        // 見たかんじ、どちらかというとひらがななのでこっちに入れておく
        (0x1B000 <= unicodes[0] && unicodes[0] <= 0x1B0FF) ||
        (0x1B150 <= unicodes[0] && unicodes[0] <= 0x1B152)
      );
    },
    isMaybeJapanese: (unicodes) => {
      return UnicodeUtils.isExtraKanji(unicodes) || UnicodeUtils.isCJKKanji(unicodes) || UnicodeUtils.isKatakana(unicodes) || UnicodeUtils.isHiragana(unicodes);
    }
  };

  const MovingUtils = {
    insertQuery: (url) => {
      const key = 'hl';

      const currentUrl = new URL(url);
      currentUrl.searchParams.set(key, JP_QUERY[key]);
      return currentUrl.href;
    },
    removeQuery: (url) => {
      const key = 'hl';

      const currentUrl = new URL(url);
      if (currentUrl.searchParams.get(key) === JP_QUERY[key]) {
        currentUrl.searchParams.delete(key);
        return currentUrl.href;
      }
      return url;
    },
    redirect: (targetUrl) => {
      location.href = targetUrl;
    }
  };

  const isSetHlJa = (url) => {
    const currentUrl = new URL(url);

    const searchParams = currentUrl.searchParams;
    const hlQuery = searchParams.get('hl');
    return hlQuery === JP_QUERY['hl']
  }

  const isJapaneseSearchTerms = (url) => {
    const currentUrl = new URL(url);

    const searchParams = currentUrl.searchParams;

    const tabMenuQuery = searchParams.get('tbm');
    if (!tabMenuQuery) { return false; }
    if (tabMenuQuery !== 'isch') { return false; }

    const searchQuery = searchParams.get('q');
    if (!searchQuery) { return false; }

    const segmenter = new Intl.Segmenter();
    const segments = segmenter.segment(searchQuery);
    const wellSegmented = [...segments];
    const maybeJapaneseLanguageContained = wellSegmented.map(s => s.segment).map(UnicodeUtils.letterToUnicodes).some(UnicodeUtils.isMaybeJapanese);
    return !!maybeJapaneseLanguageContained;
  }

  // for debug
  // _test();

  const move = (url) => {
    const hasHlJa = isSetHlJa(url);
    const isJapanese = isJapaneseSearchTerms(url);

    // 日本語っぽいクエリが入っていて、hl=jaでもないときは、hl=jaをつけてリダイレクト
    if (isJapanese && !hasHlJa) {
      MovingUtils.redirect(MovingUtils.insertQuery(url));

    // 日本語っぽいクエリが入っていないときはhl=jaは消す
    } else if (!isJapanese && hasHlJa) {
      const prevHref = url;
      const advancedHref = MovingUtils.removeQuery(prevHref);
      (prevHref !== advancedHref) && MovingUtils.redirect(advancedHref);
    }
  }

  let oldHref = location.href;
  const observer = new MutationObserver(mutations => {
    mutations.forEach(() => {
      if (oldHref !== location.href) {
        oldHref = location.href;
        move(location.href);
      }
    });
  });
  observer.observe(document.body, { childList: true, subtree: true });

  // Initial
  move(location.href);
})();

コードの説明:
https://twitter.com/harukaeru1981/status/1621951344960741376

使いたい人へ: tampermonkeyで入れてください
動作保証は特にしていません