changed

            <label for="">ホスト</label>
to
            <label for="">{{ t('app_setting.Host') }}</label>

lib/views/admin/app.html

@@ -96,7 +96,7 @@
         <div class="form-group">
           <label class="col-xs-3 control-label">{{ t('app_setting.SMTP settings') }}</label>
           <div class="col-xs-4">
-            <label for="">ホスト</label>
+            <label for="">{{ t('app_setting.Host') }}</label>
             <input class="form-control" type="text" name="settingForm[mail:smtpHost]"   value="{{ settingForm['mail:smtpHost']|default('') }}">
           </div>
           <div class="col-xs-2">