Change the language settings for Entra ID and Microsoft 365 service for all users?

Check https://learn.microsoft.com/en-us/microsoft-365/troubleshoot/access-management/set-language-and-region it is very well explained in there. You can set a preferred language for your tenant, and you can set specific language per user. Exchange mailboxes will need to be set too.

List of ISO-639 language codes in https://en.wikipedia.org/wiki/List_of_ISO_639_language_codes

I hope it helps.

Hi @Dave Leafa   

Thank you for sharing your issue on Microsoft Q&A.  

I understand that you are trying to change the language region for all users and devices in Entra ID tenant. Changing language and region settings for all users and devices in Microsoft Entra (Azure AD) is not possible in the same way as with Group Policy Objects (GPO) in on-premises Microsoft Entra.

In on-prem AD, you can centrally manage language, time zones, and regional settings using GPOs. However, Microsoft Entra is a cloud-based service that doesn’t provide GPO-style management for these settings. Instead, language and region settings in Microsoft Entra are typically configured at the user level for Microsoft 365 services (like OneDrive, SharePoint, Teams), and device settings are managed separately, usually through Intune for managed devices.   

For More information refer this links: Set language and regional settings for Microsoft 365 - Microsoft 365 | Microsoft Learn   

Language customization in Microsoft Entra user flows - Microsoft Entra External ID | Microsoft Learn      
Hope this helps. Do let us know if you have any further queries.    

If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.

Best Regards.
Harshitha Eligeti.