The Russians didn't stick to any conventions during the First and Second World Wars. They haven't even signed it yet. Besides, had the Russians ever made a declaration of war? After all, they have waged about 300 wars against their neighbors since Tsar Peter. Zhukov writes z. B. about the attack he himself led on the Japanese in Manchuria in August 1939 of an undeclared war. The attack on Germany, Austria and Turkey in 1914 after covert mobilization was not preceded by a declaration of war.
Never trust a Russian !