SET @start_global_value = @@global.lc_messages;
SELECT @start_global_value;

#
# exists as global and session
#
select @@global.lc_messages;
select @@session.lc_messages;
show global variables like 'lc_messages';
show session variables like 'lc_messages';
select * from information_schema.global_variables where variable_name='lc_messages';
select * from information_schema.session_variables where variable_name='lc_messages';

#
# show that it's writable
#
set global lc_messages=1;
select @@global.lc_messages;
set session lc_messages=2;
select @@session.lc_messages;
set global lc_messages="en_US";
select @@global.lc_messages;
set session lc_messages="en_GB";
select @@session.lc_messages;

#
# incorrect types
#
--error ER_WRONG_TYPE_FOR_VAR
set global lc_messages=1.1;
--error ER_WRONG_TYPE_FOR_VAR
set global lc_messages=1e1;

SET @@global.lc_messages = @start_global_value;
SELECT @@global.lc_messages;