There is no such thing as "highly illegal" international law... international law is just a set of conventions, and are enforced by each nation choosing what to do about the 'violation'. There aren't a set of prescribed penalties, and if there were, there is no one to enforce them.

I guess there is no international penal code. There are treaties but for many of them, there is no enforcement-no worldwide police to knock on your door.

So repercussions tend to range from nothing, through wagging fingers, slaps on the wrist, to sanctions, UN resolutions, UN-sanctioned wars, or if you really piss someone off, non-sanctioned wars.

I don’t think Belarus will be invaded, and I guess Russia would veto any particularly nasty move in the UN, so really this leaves stern words and some unilateral sanctions against the Lukshenko regime. Doesn’t seem like overwhelming penalty (though well-targeted and enforced sanctions can bite quite badly).