[N]'language' | @language_var

Is the name of the language as stored in sys.syslanguages. This argument can be either Unicode or DBCS converted to Unicode. To specify a language in Unicode, use N'language'. If specified as a variable, the variable must be sysname.

The setting of SET LANGUAGE is set at execute or run time and not at parse time.

SET LANGUAGE implicitly sets the setting of SET DATEFORMAT.

Requires membership in the public role.

The following example sets the default language to Italian, displays the month name, and then switches back to us_english and displays the month name again.

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

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