Issue #1974048 by Gábor Hojtsy, vijaycs85, er.pushpinderrana, Sutharsan, penyaskito, bserem: Fixed Limited display of languages when going back in installer is confusing.

core/lib/Drupal/Core/Installer/Form/SelectLanguageForm.php

@@ -45,21 +45,19 @@ class SelectLanguageForm extends FormBase {
     // Build a select list with language names in native language for the user
     // to choose from. And build a list of available languages for the browser
     // to select the language default from.
-    if (count($files)) {
-      // Select lists based on available language files.
-      foreach ($files as $langcode => $uri) {
-        $select_options[$langcode] = isset($standard_languages[$langcode]) ? $standard_languages[$langcode][1] : $langcode;
-        $browser_options[] = $langcode;
-      }
-    }
-    else {
     // Select lists based on all standard languages.
     foreach ($standard_languages as $langcode => $language_names) {
       $select_options[$langcode] = $language_names[1];
-        $browser_options[] = $langcode;
+      $browser_options[$langcode] = $langcode;
+    }
+    // Add languages based on language files in the translations directory.
+    if (count($files)) {
+      foreach ($files as $langcode => $uri) {
+        $select_options[$langcode] = isset($standard_languages[$langcode]) ? $standard_languages[$langcode][1] : $langcode;
+        $browser_options[$langcode] = $langcode;
       }
     }
-
+    asort($select_options);
     $request = Request::createFromGlobals();
     $browser_langcode = UserAgent::getBestMatchingLangcode($request->server->get('HTTP_ACCEPT_LANGUAGE'), $browser_options);
     $form['langcode'] = array(
@@ -70,8 +68,6 @@ class SelectLanguageForm extends FormBase {
       // Use the browser detected language as default or English if nothing found.
       '#default_value' => !empty($browser_langcode) ? $browser_langcode : 'en',
     );
-
-    if (empty($files)) {
     $form['help'] = array(
       '#type' => 'item',
       '#markup' => String::format('<p>Translations will be downloaded from the <a href="http://localize.drupal.org">Drupal Translation website</a>.
@@ -84,7 +80,6 @@ class SelectLanguageForm extends FormBase {
         ),
       ),
     );
-    }
     $form['actions'] = array('#type' => 'actions');
     $form['actions']['submit'] =  array(
       '#type' => 'submit',

core/modules/system/src/Tests/Installer/InstallerLanguagePageTest.php

@@ -0,0 +1,49 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\system\Tests\Installer\InstallerLanguagePageTest.
+ */
+
+namespace Drupal\system\Tests\Installer;
+
+use Drupal\simpletest\InstallerTestBase;
+
+/**
+ * Verifies that the installer language list combines local and remote languages.
+ *
+ * @group Installer
+ */
+class InstallerLanguagePageTest extends InstallerTestBase {
+
+  /**
+   * Installer step: Select language.
+   */
+  protected function setUpLanguage() {
+    // Place a custom local translation in the translations directory.
+    mkdir(DRUPAL_ROOT . '/' . $this->siteDirectory . '/files/translations', 0777, TRUE);
+    touch(DRUPAL_ROOT . '/' . $this->siteDirectory . '/files/translations/drupal-8.0.0.xoxo.po');
+
+    // Check that all predefined languages show up with their native names.
+    $this->drupalGet($GLOBALS['base_url'] . '/core/install.php');
+    foreach (\Drupal::languageManager()->getStandardLanguageList() as $langcode => $names) {
+      $this->assertOption('edit-langcode', $langcode);
+      $this->assertRaw('>' . $names[1] . '<');
+    }
+
+    // Check that our custom one shows up with the file name indicated language.
+    $this->assertOption('edit-langcode', 'xoxo');
+    $this->assertRaw('>xoxo<');
+
+    parent::setUpLanguage();
+  }
+
+  /**
+   * Confirms that the installation succeeded.
+   */
+  public function testInstalled() {
+    $this->assertUrl('user/1');
+    $this->assertResponse(200);
+  }
+
+}