日本語・英語と設定の保存

function detectLang() {
  // 共有された ?lang=en などのアドレスで開いた時は、その言語を保存した設定より優先する(保存はしない)。
  try {
    const asked = /[?&]lang=([a-z]+)/.exec(location.search)?.[1];
    if (Object.hasOwn(STRINGS, asked)) return asked;
  } catch (e) {}
  try {
    const saved = localStorage.getItem(LANG_KEY);
    if (Object.hasOwn(STRINGS, saved)) return saved;
  } catch (e) {}
  const tag = typeof navigator !== "undefined" ? String(navigator.language || "") : "";
  return tag.toLowerCase().startsWith("ja") ? "ja" : "en";
}

function T(key, ...args) {
  const v = STRINGS[lang][key];
  return typeof v === "function" ? v(...args) : v;
}

function applyLang(next) {
  if (next && next !== lang) {
    lang = next;
    try { localStorage.setItem(LANG_KEY, lang); } catch (e) {}
  }
  if (document.documentElement) document.documentElement.lang = lang;
  const hintEl = document.getElementById("hint");
  if (hintEl) hintEl.innerHTML = T("hint").join("<br>");
  const shareEl = document.getElementById("shareLink");
  if (shareEl) {
    const share = SHARE[lang];
    shareEl.href = `https://x.com/intent/post?text=${encodeURIComponent(share.text)}&url=${encodeURIComponent(share.url)}`;
    document.getElementById("shareLabel").textContent = share.label;
  }
  for (const code in langButtons) langButtons[code].setAttribute("aria-pressed", String(code === lang));
  refreshActionButtons();
  redrawIfPaused();
}