You can't change your original configuration's language from your default language. However, if you need a configuration in a different language, you can create a new configuration.
To add a language-specific branding configuration
Sign in to the Azure portal using a Global administrator account for the directory.
Select Azure Active Directory, and then select Company branding, and then select New language.
On the Configure company branding page, select your language (for example, French) and then add your translated information, based on the descriptions in the Customize your Azure AD sign-in page section of this article.
The Contoso – Company branding page updates to show your new French configuration.