What are DATEFIRST's default values for non-US English languages in SQL Server?

SQL Server has a DATEFIRST setting that determines the first day of the week for date calculations.

SELECT DATENAME(weekday, '2025-04-23') AS WeekdayName  -- Wednesday

SET DATEFIRST 7  -- Sunday
SELECT DATEPART(weekday, '2025-04-23') AS WeekdayNumber  -- 4

SET DATEFIRST 1  -- Monday
SELECT DATEPART(weekday, '2025-04-23') AS WeekdayNumber  -- 3

According to Microsoft's documentation, the default value of DATEFIRST in U.S. English is 7 (Sunday).

If SQL Server is configured with a non-English or non-US language, will the default value of DATEFIRST be something other than 7? If so, how do I check the default values for different languages?

Yes, they are different.

You can get the current session's setting from @@DATEFIRST. If you want to see what the different languages default to, query sys.syslanguages:

SELECT datefirst,
       name,
       alias
FROM sys.syslanguages;

In SQL Server 2022, this gives the following results:

db<>fiddle