With over 300,000 installs, Polylang is the most popular multilingual plugin available on the WordPress directory. You write your posts, pages and create categories and post tags as usual, and assign a language to each of them.
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.
A better way of translating your WordPress site directly from the front-end, with full support for WooCommerce, complex themes and site builders. A WordPress translation plugin that's easy to use for a change.