Ensure select2 is initialized regardless of page load events

Previously, select2 was only loaded successfully, if first the page was loaded (turbolinks:load) and then all select2 locales (select2:locales:loaded). However, if the order was different, select2 wouldn't be initialized.

Fixes #1476

app/javascript/application.js

@@ -50,8 +50,15 @@ import locales from "../../tmp/locales.json";
 
 Promise.all(
     Object.keys(locales).map(locale => import(`select2/dist/js/i18n/${locale}`))
-).then(() =>
-    document.dispatchEvent(new Event("select2:locales:loaded"))
+).then(() => {
+    // Since there is a race condition between the locales and turbolinks,
+    // we don't know whether the locales are loaded before or after turbolinks.
+    // Therefore, we trigger the event in both cases.
+    $(document).on('turbolinks:load', () =>
+      $(document).trigger('select2:locales:loaded')
+    );
+    $(document).trigger('select2:locales:loaded')
+  }
 );
 
 // Fetch user locale from html#lang.