If you are using OSX this AppleScript will change all the style definitions and text for the active document to French. Just edit the first line for the desired language so Canadian English would be: set lang to "English: Canadian"
set lang to "French"
tell application "Adobe InDesign CS6"
set pstyles to all paragraph styles of active document
repeat with i from 1 to number of items in pstyles
try
set applied language of item i of pstyles to lang
end try
end repeat
set cstyles to all character styles of active document
repeat with i from 1 to number of items in cstyles
try
set applied language of item i of cstyles to lang
end try
end repeat
try
set applied language of every paragraph of every story of active document to lang
end try
end tell