This little one is really hard.
That was the intention
Time for some hints:
It's neither french nor german, but "prototype" fits in that WW2 stopped further development and production of this little trainer aircraft and only two could be produced.
The picture shows aircraft no.1 at Paris Air Show in 1938, with retouched background (not retouched by me, but by the manufacturer).
Last but not least, this is the engine:
Best regards - Mike