The 'download_translation' flag in install_state_defaults is not respected during install

A fix from me for this is to check the flag value and pass the server_pattern only if the flag 'download_translation' is TRUE, in the file core/includes/install.core.inc:

  // Check whether all conditions are met to download. Download the translation
  // if possible and enabled.
  $server_pattern = $install_state["download_translation"]
    ? $install_state['server_pattern']
    : NULL;

  $requirements = install_check_translations($install_state['parameters']['langcode'], $server_pattern);

- see the MR https://git.drupalcode.org/project/drupal/-/merge_requests/9900

After this, the installing time for non-en languages decreased to almost the same as with en language. But still not equal, so seems it still spends time on scanning files or other operations.

This issue causes slow performance of running all tests with non-default language, I reported this as a separate issue: #3482349: drupalInstall Nightwatch command with non-default langcode takes too long time to install

The same issue is true for functional tests using Simpletest and PHPUnit.

Here are tests of the Nightwatch drupalInstall() on the 11.x branch:

  ℹ Loaded url http://web in 203ms
drupalInstall default time: 3.367 seconds
  ℹ Loaded url http://web in 94ms
drupalInstall fr time: 26.343 seconds
  ℹ Loaded url http://web in 124ms
drupalInstall en time: 4.505 seconds
  ℹ Loaded url http://web in 111ms
drupalInstall de time: 35.939 seconds

and with my fixes:

  ℹ Loaded url http://web in 212ms
drupalInstall default time: 5.515 seconds
  ℹ Loaded url http://web in 114ms
drupalInstall fr time: 8.656 seconds
  ℹ Loaded url http://web in 97ms
drupalInstall en time: 4.087 seconds
  ℹ Loaded url http://web in 91ms
drupalInstall de time: 7.93 seconds

So, at least we got speed up for 5+ times! But still not the same time as with the en language.

The Nightwatch test code to measure on your side:

module.exports = {
  'Compare drupalInstall time with languages': async (browser) => {
    let startTime;

    await browser.pause(5000)

    startTime = new Date();
    await browser.drupalInstall();
    console.log(
      `drupalInstall default time: ${(new Date() - startTime) / 1000} seconds`,
    );
    await browser.drupalUninstall();
    await browser.pause(5000)

    startTime = new Date();
    await browser.drupalInstall({ langcode: 'fr' });
    console.log(
      `drupalInstall fr time: ${(new Date() - startTime) / 1000} seconds`,
    );
    await browser.drupalUninstall();
    await browser.pause(5000)

    startTime = new Date();
    await browser.drupalInstall({ langcode: 'en' });
    console.log(
      `drupalInstall en time: ${(new Date() - startTime) / 1000} seconds`,
    );
    await browser.drupalUninstall();
    await browser.pause(5000)

    startTime = new Date();
    await browser.drupalInstall({ langcode: 'de' });
    console.log(
      `drupalInstall de time: ${(new Date() - startTime) / 1000} seconds`,
    );
    await browser.drupalUninstall();
  },
};

Tested on my tests and it works great, so moving to the "Needs review".