use t for the validation alert 2

resource/locales/en-US/translation.json

@@ -101,6 +101,10 @@
   "Deleted Pages": "Deleted Pages",
   "Sign out": "Logout",
 
+  "form_validation": {
+    "required": "<code>%s</code> is required"
+  },
+
   "installer": {
     "setup": "Setup",
     "create_initial_account": "Create an initial account",

resource/locales/ja/translation.json

@@ -118,6 +118,10 @@
   "Deleted Pages": "削除済みページ",
   "Sign out": "ログアウト",
 
+  "form_validation": {
+    "required": "<code>%s</code> に値を入力してください"
+  },
+
   "installer": {
     "setup": "セットアップ",
     "create_initial_account": "最初のアカウントの作成",

src/server/crowi/express-init.js

@@ -153,4 +153,9 @@ module.exports = function(crowi, app) {
   }
 
   app.use(i18nMiddleware.handle(i18next));
+
+  app.use(function(req, res, next) {
+    crowi.t = req.t;
+    next();
+  });
 };

src/server/routes/admin.js

@@ -1496,7 +1496,8 @@ module.exports = function(crowi, app) {
     for (const key of crowi.passportService.mandatoryConfigKeysForSaml) {
       const formValue = form.settingForm[key];
       if (crowi.configManager.getConfigFromEnvVars('crowi', key) === null && formValue === '') {
-        form.errors.push(`${key} is required`);
+        const formItemName = crowi.t(`security_setting.form_item_name.${key}`);
+        form.errors.push(crowi.t('form_validation.required', formItemName));
       }
     }
   }