Since version 4.0, WordPress has offered language selection within the installation process. That language then becomes the one and only language of the site.
If you want to have posts, pages, and custom post types available in multiple languages, you will need a translation plugin to handle the extra functionality. Translation plugins allow you to translate the content (often by hand, manually) into numerous other languages.
Then when your users come to the site, they can pick which language to view the post in.
Luckily there’s an array of great translation plugins available for WordPress, and we’ve rounded up the top 4 along with their guides on translating custom fields with ACF