Danish characters are not translated correctly with transliteration

I confirmed that the langcode for Denmark is "da" (see attachment). Country code for Denmark is "DK" core/lib/Drupal/Core/Locale/CountryManager.php. It could have been misleading.

'DJ' => t('Djibouti'),
'DK' => t('Denmark'),
'DM' => t('Dominica'),

However, for backwards compatibility it might be better to just add a new file named 'da.php', since people might have added their own workarounds.

I think we should leave only one version, but I may be wrong. In the new patch, "dk.php" is deleted.

PhpTransliterationTest.php also needs updating:

['dk', $two_byte, 'A O U Aa Oe aouaaoehello'],
['dk', $random, $random],

I think I agree with the assesment that we should leave the wrong file behind, and use @trigger_error to mark it as deprecated. I'm not sure, so setting this to rtbc to bring this to maintainer attention.

If we don't want to do the trigger error, this looks good to go

If we delete the wrong "dk.php" file it will never break the transliteration, because the following code (core/lib/Drupal/Component/Transliteration/PhpTransliteration.php) checks if the file exists:

protected function readLanguageOverrides($langcode) {
  // Figure out the file name to use by sanitizing the language code,
  // just in case.
  $file = $this->dataDirectory . '/' . preg_replace('/[^a-zA-Z\-]/', '', $langcode) . '.php';

  // Read in this file, which should set up a variable called $overrides,
  // which will be local to this function.
  if (is_file($file)) {
    include $file;
  }
  if (!isset($overrides) || !is_array($overrides)) {
    $overrides = [$langcode => []];
  }
  $this->languageOverrides[$langcode] = $overrides[$langcode];
}

Possible solutions used so far by programmers:

1. Adding "da.php" file with patch #4 or creating a similar custom patch (probably the most common).
2. Extend class PhpTransliteration in custom module with following code:

protected function readLanguageOverrides($langcode) {
  // Figure out the file name to use by sanitizing the language code,
  // just in case.
  $file = $this->dataDirectory . '/' . preg_replace('/[^a-zA-Z\-]/', '', $langcode) . '.php';

  // Incorrect file in Danish translation
  if (!is_file($file) && $langcode == 'da') {
    $file = $this->dataDirectory . '/dk.php';
  }

  // Read in this file, which should set up a variable called $overrides,
  // which will be local to this function.
  if (is_file($file)) {
    include $file;
  }
  if (!isset($overrides) || !is_array($overrides)) {
    $overrides = [$langcode => []];
  }
  $this->languageOverrides[$langcode] = $overrides[$langcode];
}

What will happen if we remove wrong file:

In the first case, after the core update (e.g. to 8.7), Composer will inform you that the patch #4 could not be applied. It is safe.
In the second case, one or the other file will be used, so it is also safe.

That's why we probably do not have to leave a wrong file.

The last submitted patch, 8: core_transliteration-danish-incorrect-2895315-8-D8.patch, failed testing. View results

I launched the re-test. It's pass.

Back to rtbc, with the same remarks as #10.

This should be fixed in the dev branch first.

We should be fine to remove the old file, it will never be found unless someone configures a custom 'dk' language, and it's data rather than an API as such. However, given that, only committing this to 8.7.x so it comes out in a minor release.

Committed 2580766 and pushed to 8.7.x. Thanks!