You are correct that a string literal date with separators is not multi-language compatible, but it is DATEFORMAT independent. My example should be revised to use unseparated 'CCYYMMDD' format,...

The code as I submitted it works correctly, including the date string literal. The format for the date string literal argument to the function is ISO 8601 ANSI SQL...

SELECT DATENAME(weekday, 'CCYY-MM-DD') does it for me. I would hope that this builtin function handles different DATEFIRST settings correctly.