Yes, as a French foreigner too, I tried to respect as much as possible the "official" terms, but I agree with you, "Gyrophares" sounds so... mainstream xD
And I find Amercian police better than ours, anyway I play with the English translation for a better role-play !
It's a very good idea! I can suggest you a French translation :
Sound : Sirène
Lights : Lumière
Traffic Stop : Contrôle Routier
I'm impatient to see next updates!