Cldr.Config.known_locale_names

You're seeing just the function known_locale_names, go back to Cldr.Config module for more information.
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known_locale_names(backend)

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Specs

known_locale_names(t() | Cldr.backend()) :: [Cldr.Locale.locale_name()]

Returns a list of all locales that are configured and available in the CLDR repository.