Ok. Is there an easy way to make more voices say "Langen Radar" instead of "Dusseldorf" than only (haven't tried all of course) German Pilot 1?
No there isn't. The only way to do it is to create a new wav file but cutting and pasting sylables from other wav files to make the sound you require. It would also have to be done 238 times!

That particular author (German pilot #1) took it upon himself to record '
Langen Rader' because, rightly or wrongly, the script at the time specified 'Dusseldorf Radar'. Had I spotted it back then I would have told him to change it.