Is the electrician's work correct?

Hello everyone,

I looked at the electrician's work today. At one point where 7x1.5mm² should have been installed, 5x1.5mm² + 3x1.5mm² was installed instead. However, this would mean I am missing an L conductor. Or would the "2nd neutral conductor" of the 3x1.5mm² cable also be allowed to be used as L?

Green/Yellow and Blue are reserved for Earth and Neutral conductor

Green/yellow is definitely to be used for earth/PE, legally. Blue as neutral conductor is nice to have, but may certainly be used as a switching conductor or similar. So what your electrician is doing is absolutely fine. At least that was still the case during my apprenticeship (8 years ago).

Green/yellow and blue are reserved for earth and neutral conductor

Blue as neutral conductor is nice to have, but can definitely be used as a switched wire or similar.

Hmm, now I have 2 opposing opinions o_O
Unfortunately, I haven't found anything about it on Google either.

There is no legal requirement (as far as I remember) that blue must be the neutral conductor.