Why do pilots say "roger" on the radio?

Pilots and other military types say “roger” to acknowledge receipt of a message or instructions. “Roger” at one time was the phonetic designation for the letter R, which in turn stood for “received.” Why not just say "received"? From a safety perspective, it makes sense to use standardized language, particularly when dealing with international operations. An American pilot may not understand German, but they both understand aviation terminology. The International Civil Aviation Organization oversees this standardization and disseminates it accordingly.

WORLD NEWS: Why do pilots say "roger" on the radio?