How do I determine a public holiday in Sql server?

I just gather information over the internet and I come with this easy way to calculate the US Bank Holidays.

US Bank Holidays

===========================

DECLARE @Year char(4)
, @Date datetime
, @Holiday datetime

SET @Year = 2010

---- New Years Day
SET @Date=CONVERT( datetime, CONVERT(varchar, YEAR( @Year ) )+'-01-01' ) 
IF DATENAME( dw, @Date ) = 'Saturday'
    SET @Date=@Date-1
ELSE IF DATENAME( dw, @Date ) = 'Sunday'
    SET @Date=@Date+1
SELECT @Date [New Years Day], DATENAME( dw, @Date ) [DayOfWeek]

---- Martin L King's Birthday ( 3rd Monday in January )
SET @Date = CONVERT( datetime, CONVERT(varchar, YEAR( @Year ) )+'-01-01' ) 
SET @Holiday = DATEADD( wk, DATEDIFF( wk, 0, dateadd( dd, 18-datepart( day, @Date ), @Date ) ), 0 ) -- 3rd Monday of the Month
SELECT @Holiday [Martin L King's Birthday], DATENAME( dw, @Holiday ) [DayOfWeek]

---- President’s Day ( 3rd Monday in February )
SET @Date = CONVERT( datetime, CONVERT(varchar, YEAR( @Year ) )+'-02-01' ) 
SET @Holiday = DATEADD( wk, DATEDIFF( wk, 0, dateadd( dd, 18-datepart( day, @Date ), @Date ) ), 0 ) -- 3rd Monday of the Month
SELECT @Holiday [President’s Day], DATENAME( dw, @Holiday ) [DayOfWeek]

---- Memorial Day ( Last Monday in May )
SET @Date = CONVERT( datetime, CONVERT(varchar, YEAR( @Year ) )+'-05-01' ) 
SET @Holiday = DATEADD( wk, DATEDIFF( wk, 0, dateadd( dd, 30-datepart( day, @Date ), @Date ) ), 0 ) -- 5th Monday of the Month
SELECT @Holiday [Memorial Day], DATENAME( dw, @Holiday ) [DayOfWeek]

---- Independence Day ( July 4 )
SET @Date=CONVERT( datetime, CONVERT(varchar, YEAR( @Year ) )+'-07-04' ) 
IF DATENAME( dw, @Date ) = 'Saturday'
    SET @Date=@Date-1
ELSE IF DATENAME( dw, @Date ) = 'Sunday'
    SET @Date=@Date+1
SELECT @Date [Independence Day], DATENAME( dw, @Date ) [DayOfWeek]

---- Labor Day ( 1st Monday in September )
SET @Date = CONVERT( datetime, CONVERT(varchar, YEAR( @Year ) )+'-09-01' ) 
SET @Holiday = DATEADD( wk, DATEDIFF( wk, 0, dateadd( dd, 6-datepart( day, @Date ), @Date ) ), 0 ) -- 1st Monday of the Month
SELECT @Holiday [Labor Day], DATENAME( dw, @Holiday ) [DayOfWeek]

---- Columbus Day ( 2nd Monday in October )
SET @Date = CONVERT( datetime, CONVERT(varchar, YEAR( @Year ) )+'-10-01' ) 
SET @Holiday = DATEADD( wk, DATEDIFF( wk, 0, dateadd( dd, 12-datepart( day, @Date ), @Date ) ), 0 ) -- 2nd Monday of the Month
SELECT @Holiday [Columbus Day], DATENAME( dw, @Holiday ) [DayOfWeek]

---- Veteran’s Day ( November 11 )
SET @Date=CONVERT( datetime, CONVERT(varchar, YEAR( @Year ) )+'-11-11' ) 
IF DATENAME( dw, @Date ) = 'Saturday'
    SET @Date=@Date-1
ELSE IF DATENAME( dw, @Date ) = 'Sunday'
    SET @Date=@Date+1
SELECT @Date [Veteran’s Day], DATENAME( dw, @Date ) [DayOfWeek]

---- Thanksgiving Day ( 4th Thursday in November )
SET @Date = CONVERT( datetime, CONVERT(varchar, YEAR( @Year ) )+'-11-04' ) 
SET @Holiday = DATEADD( wk, DATEDIFF( wk, 0, dateadd( dd, 22-datepart( day, @Date ), @Date ) ), 0 )+3 -- 4th Thursday of the Month
SELECT @Holiday [Thanksgiving Day], DATENAME( dw, @Holiday ) [DayOfWeek]

---- Christmas Day ( December 25 )
SET @Date=CONVERT( datetime, CONVERT(varchar, YEAR( @Year ) )+'-12-25' ) 
IF DATENAME( dw, @Date ) = 'Saturday'
    SET @Date=@Date-1
ELSE IF DATENAME( dw, @Date ) = 'Sunday'
    SET @Date=@Date+1
SELECT @Date [Christmas Day], DATENAME( dw, @Date ) [DayOfWeek]

---- New Years Eve Day
SET @Date=CONVERT( datetime, CONVERT(varchar, YEAR( @Year ) )+'-12-31' ) 
IF DATENAME( dw, @Date ) = 'Saturday'
    SET @Date=@Date-1
ELSE IF DATENAME( dw, @Date ) = 'Sunday'
    SET @Date=@Date+1
SELECT @Date [New Years Day], DATENAME( dw, @Date ) [DayOfWeek]

Isn't a public holiday very dependent of locale?

Programatically, there is no way to compute this. Alternatively, you will need to find an official list of holidays for each of your locales. And even so, you will not get the granularity you want.

As far as I know there isn't any 'official' source, and this is indeed highly dependent on locale. You'd have to manage these manually. A good source seems to be:

http://en.wikipedia.org/wiki/List_of_holidays_by_country

Even under these circumstances it's very tricky to manage. For example, I live in Belgium, and different parts of the country have different holidays. Government workers for example have different holidays compared to the rest of the workforce, and this is in the same locale code.

In our applications we have it part of the user configuration. There is a place for users to set what they consider public/bank holidays for as far into the future as they want. For ease of use there is the ability to copy them by date from previous years. This also allows them to set 'custom' public holdays, perhaps a day that the company treats as a holiday but is not natioanlly official...

Programatically, however, there are absolutely no assumptions at all. It's effectively just a user maintained table of dates.

(This includes the UK because, as stated above, some holidays vary and are not set in stone, and sometimes there are special one-off days.)

Public holidays are rarely available for the next 50 years. In some countries they are known for the next couple of years, in some countries not. They also vary by states and even cities.