Click on the language you want to download (below), and save the .zip file to a temporary directory on your hard drive.
Unzip the file into the same location. You'll see an appropriately named directory (either American, British, or German) containing hundreds of .wav files.
Go to the Combat Flight Simulator directory that contains the radio chatter files and rename the existing language directory.

The default setup location of the radio chatter files is: C:\Program Files\Microsoft Games\Combat Flight Simulator\Sound\Radio\American, British, or German.

For example, if you are replacing the German radio files, rename the German directory to German_old.

Copy the entire unzipped directory of files from the temporary directory into the Radio directory in your CFS installation. That's it, you're done.

Note: The wav files on the CFS CD are not directly compatible, as the file names are expanded during setup. And, if you replace a set of radio chatter files with the corresponding set of files in another language, the screen text associated with those new files will also be in the native language as well. The German, British, and American Radio Chatter files are not supported by Microsoft Product Support.