function languageChange() {
  // Store the blocks in sessionStorage for the duration of the reload.
  const text = JSON.stringify(
    Blockly.serialization.workspaces.save(Blockly.getMainWorkspace()),
  );
  try {
    window.sessionStorage.setItem('loadOnceBlocks', text);
  } catch (e) {
    // Storage can be flakey.
    console.log(e);
  }

  const newLang = document.getElementById('languageDropdown').value;
  window.location.search = '?hl=' + encodeURIComponent(newLang);
}
Change the (human) language.  Reloads the page.