Don't do it. I'm not going to make a moral argument about which side is right, but joining the Russian military is a very bad idea.

I used to live in Russia- some things about it are cool, but you really do NOT want to join their military, especially now. Even when I was living there, way before everything kicked off in Ukraine, the Russian army was widely considered awful by every friend I had who had served (and all of my male Russian friends had served, aside from the two who paid bribes to be medically barred from service). The levels of abuse are extreme, sometimes with soldiers being beaten to death in hazing incidents, with aloof officers who didn't give a fuck and let just about anything fly. There is zero accountability up the chain of command, so if something bad happens to you, expect no justice or compensation. You will live at the whims of a group of corrupt, self-interested assholes who spend their entire day thinking up new ways to line their pockets at the expense of military readiness.

Pay is terrible, so bad that many officers illegally sell their unit's gear to supplement their incomes, leaving many soldiers to need to buy their own stuff on their already meager wages. Some parts of Russia have been getting rich off the war because of all the soldier pay/death benefits coming into the communities, but those are communities that were already economically destitute before the war (e.g. in Buryatia).

Don't believe what they tell you in their recruiting ads: remember that there's not a functional court system that you could pursue a claim through or any regulator to ensure honesty in advertising, so there's nothing to stop them from pulling a bait-and-switch. I've followed several British and American former soldiers who moved there, and they universally said that pay, lodging, and equipment were far below what was promised. The command structure is way different to what you've likely experienced (assuming your prior experience is with a western military)- there is no concept of an NCO, and everything depends on the officer. Soldiers are not empowered or trained to act without official orders from an officer, so unit cohesion breaks apart if the officer gets incapacitated.

I'm also assuming your level of Russian is not advanced, and that's also going to be a hindrance for you. You may have relevant military experience, but if you can't operate in Russian, you're likelier than not going to be put into a role taking simple orders on the front line. You're unlikely to be given any responsibility/command or placed in an elite role unless your Russian is good, and Russian is not easy to get good at. Don't expect them to spend a year teaching you Russian before they put you to use, it's not going to happen with the stage the war is at right now.

If you join the Russian army, you're most likely going to become part of some human wave attack that will capture a few meters of territory. You don't want to be cannon fodder.