[sql-server] How to change default language for SQL Server?

Please try below:

DECLARE @Today DATETIME;  
SET @Today = '12/5/2007';  

SET LANGUAGE Italian;  
SELECT DATENAME(month, @Today) AS 'Month Name';  

SET LANGUAGE us_english;  
SELECT DATENAME(month, @Today) AS 'Month Name' ;  
GO  

Reference:

https://docs.microsoft.com/en-us/sql/t-sql/statements/set-language-transact-sql