There have been a lot of foreign volunteers on both sides of this conflict.
Seems to be quite a number of Serbs fighting alongside the Russians. No idea what Serbian law (if any) says about this.
It makes a difference which side you are fighting for, our side, or for the enemy, Spain is a part of our NATO alliance, and these traitors were supporting Russia.
Ah, what a surprise :)))
I wonder If these are the same clowns with funny mustaches that Kremlin propaganda were using as a kind of freak show last year... I guess they wanted to give it “international anti-fascist movement” outlook or something... but apparently they finally realized it was too stupid even by their (your) standards, so they pushed them off the payroll list.