Ghost's front-end and themes are fully translatable and the customisable dynamic routing layer unlocks multi-language content.
To set a publication language to be used for theme translations, go to the“General” settings of Ghost Admin and enter the language/locale tag to be used, e.g.
es for Spanish,
fr for French,
zh for Chinese,
ja for Japanese.
For further details on how to make your theme translatable, check out the translate handlebars helper guidelines.
Multi-language content is also supported by configuring custom collections and templates using Dynamic Routing. This allows you to render different languages on their own routes - read the tutorial for more details.