Try something like this.
If you have a XML variable:
declare @xml XML = '<locale en-US="Test & Data" />';
select
data.node.value('@en-US', 'varchar(11)') my_column
from @xml.nodes('locale') data(node);
In your case, for a table's column (sorry for not given this example first):
create table dbo.example_xml
(
my_column XML not null
);
go
insert into dbo.example_xml
values('<locale en-US="Test & Data" />');
go
select
my_column.value('(/locale/@en-US)[1]', 'varchar(11)') [en-US]
from dbo.example_xml;
go
Hope it helps.