In order to add multiple languages to your event, first go to the Settings tab of your main Event page. There, you will find the Languages section where you can start searching for a specific language and once you find it, click on the plus button next to it. In order to remove a language, click on the red Trash bin icon right next to the language listed.
Once those languages are added, they will become available in both Email marketing and Website Builder. Simply change language as shown in the image below:
In case contacts/participants selected Preferred language field, website or email or form would be shown in that selected language. In any other case, everything would be shown in the default event language.