Adding a line to a word document in multiple places

Question

I have a very large MS word document (40 or 50 pages) that is made up of similar chunks of text
English - hello
Spanish - hola
French - bonjour
English - goodbye
Spanish - adios
French - au revoir
I would like to add another language - i.e. add a German line after every French line. I dont have to worry about the content of the line - we have transaltors to do that but i would like the document to look like
English - hello
Spanish - hola
French - bonjour
German -
English - goodbye
Spanish - adios
French - au revoir
German -
So what i want the logic to say is every time there is a line that starts with "French" insert a line containing "German"
As i said there are almost a thousand of these groups so doing it by hand is not really an option.
Thanks