Each storefront has its own primary and additional languages. This lets one store use a different language selection for each domain or regional storefront.
Open Online Store and choose the storefront you want to change.
Open its language settings.
Choose the storefront's primary language and any additional languages shoppers can select.
Open Countries and assign the additional languages to every covered country where shoppers should use them, then choose one default language for each country.
Save, then preview the storefront in every published language.
The language picker lists every language already enabled for the store. Staff with Online Store access can assign those languages without Settings > Languages access. Enabling a new language for the store still happens in Settings > Languages.
Removing a language from a storefront hides it there but keeps its translations and keeps it available to other storefronts.
The primary storefront follows the default language in Settings > Languages. Add additional store-enabled languages here, then open Countries to choose the languages each covered country serves and select one default. Without an explicit country assignment, that country serves only the storefront primary language. Adding a language does not translate content.