As you're in Sweden, I presume you have 3-phase 400 V mains. This means 3 phases wtih 230 V each to neutral.
Unless your variac is rated at 400 V, connecting it to L1/L2 is a really bad idea.
And not just because of the voltage, but also the complete lack of of a neutral voltage. Variacs are not isolated from the mains.
Don't do it and stay alive.