Hello
Napoleonic Warmaster has looked at multi national armies and using lines of command is another means of control for 'mixed' armies:-
In a multi-national army, units may receive orders only from the Army General and from Heroes of their own nationality (for example, Spanish troops can receive orders from the British General commanding the army, or from any Spanish Heroes, but not from British Heroes). A Brigade containing units from several Nationalities cannot receive orders from a character unless that character can command all of the units in the Brigade. Some army lists may alter this (for example, Portuguese troops, who were trained by and lead by British officers, will be able to receive order from British Heroes). In all other respects this army fights as a single army.
Cheers
GrumpyOldMan