The linked login sample makes use of Auth0.js authorize method which means the end-user authentication will be processed through the hosted login page which is the recommended option.
Be default, the hosted login page uses Lock 10 as the interface available for end-user authentication, however, you can customize either just Lock or the complete page itself (use a custom credentials form without Lock).
In order to customize the hosted login page you need go through the Dashboard because any Lock customization options you try to pass from the client itself won’t have any effect.
In conclusion, the languageDictionary you’re trying to use should be specified in the hosted login page customization and not directly in the client application itself.