Datetime format changed

Is getting the culture language according the client when you login through windows and the server one when you login through the sql. on this post they tell that the best solution is check on the client side the culture and apply what you need (https://www.experts-exchange.com/questions/21110441/Culture-specific-date-formatting.html)

also check this
http://stackoverflow.com/questions/2432185/how-can-i-query-the-database-culture-sql-server-2005

1.How to make common language setting irrespective to the logins?

2.What determine this setting when i create the logins?

3.Through SQL logins it's british and through Window is US. How to make to it common around the logins?

Have you looked into datetimeoffset?  This gives you an "absolute" time as opposed to local/server time.  Please take a look at the following article.  It might prove to be useful.

http://blogs.msdn.com/b/bartd/archive/2009/03/31/the-death-of-datetime.aspx