Update your existing config.php
file with the following changes.
Missing those changes, errors will happen.
New config for i18n. Open config.php and add the following:
# language settings
const FRONTEND_LANGUAGE = 'en';
currently only en (default) and de are available.
To provide the correct URL please add this.
# Installation Domain. Webrootpath will be added automatically
const INSTALL_URL = 'http://localhost';