It’s not every day that two boys serenade you for your 13th birthday in a foreign language. But that’s what happened Thursday at the White Settlement home of Christina Nicholson, a member of the Texas Girls’ Choir. “Amazing,” Nicholson said, with a slight blush. “Last night at midnight, they serenaded me.” The young men doing the serenading are part of the Mexico Boys Choir, which travels to Fort Worth every summer in a musical and cultural excha…