Mysql insert fixed column value for each row during multi-insert
I am surely too late for you, but maybe somebody will have similar question in the future.

A way how to accomplish that is by creating temporary table #temptable, and while copying data to actual table, add constant column:

# en-US.sql
INSERT INTO #temptable (resource_key, resource_value) VALUES 
    ("GEN.YES", "Yes"),
    ("GEN.NO", "No"),
    ("GEN.MAYBE", "Maybe")
ON DUPLICATE KEY UPDATE `resource_value` = VALUES(`resource_value`);

INSERT INTO table (resource_key, resource_value, locale) VALUES 
    (SELECT t.*, "en-US" FROM #temptable AS t);