Let’s say you wish to create a multilingual site that serves content in several languages: English (United States), French (France), Spanish (Spain), and Japanese (Japan).
If you have set English (United States) as the master language, you will need to add French, Spanish, and Japanese manually. Learn more about adding a language to your stack.
While adding languages to your stack, you also need to specify the fallback language for each language that you add. Fallback language is the parent from which the given language inherits data from. By default, the fallback for each language is the master language. You can change this while adding languages to your stack. Learn more about fallback languages.
After first creating an entry in the master language, i.e., English (United States), when you start creating an entry in any of the added languages (e.g., 'French - France), it will show data inherited from the fallback language.
This is an unlocalized entry. Meaning it is still an entry that is fetching data from its fallback language, and a separate entry has not yet been created in the selected language.
This inheritance continues until you localize the unlocalized entry. This is called data inheritance.
Note: This logic only applies to entry creation and does not apply to entry publishing. Read more about how to publish localized/unlocalized entries here.