Strattic supports Polylang, a popular multilingual plugin for WordPress that tries to simplify managing a multilingual site. You write posts, pages and create categories and tags as usual, and then define the language for each of them.
Polylang is compatible with major SEO plugins and automatically takes care of multilingual SEO such as HTML hreflang tags and opengraph tags.
For information on setting up Polylang to work on Strattic, please refer to our documentation.