Your default language is the language in which you write original product, content, and storefront text. Other enabled languages hold translated versions of that content. Your plan sets the total number of languages you can enable, including the default language.
Enabling a language does not translate your content or immediately show the language to shoppers. It makes the language available in Translations and in each storefront's language settings. Shoppers can use it only after you add it to a storefront.
When a translation is missing, the storefront uses the original content from your default language. Complete the important customer-facing translations before publishing a language.
Before switching to a plan with a lower language limit, reduce the enabled languages to that plan's limit. The plan change is blocked while too many languages remain enabled. Once a lower plan is scheduled, you can't enable more languages than that plan includes.