Hi,
what Navigation System is this one and what function is behind the Apps Button?

 

That looks like a NON US spec TLX. It could be Russian or something. The early TLX 15-17 in those markets had a APP button, which was basically useless. Not apple CarPlay I dont think. The 16-18 ILX premium pkg in the states had the app button and only was Acura based apps, basically useless

 

The Pictrure is from the US Version. You can see it on the temperature from the climate control.
The non US Version are all in Celsius.