Is there any way to find out what happened to a post card sent from other country? [closed]

It's impossible to find out what exactly has happened with lost postcard, because it would require finding it first, so it wouldn't be lost postcard anymore...

There are many points of failure. First of all, letters in Poland do disappear. With registered letter, you can at least get some compensation in that case, and they are lost less often. But with the normal letters and postcards many things can happen.

Letters disappear in sorting facilities. If they are sorted wrongly and returned, then anything can happen. Those facilities works like washing machines on socks.

Letters got thrown into wrong postbox. Either they are thrown away, or thrown to 'unsolicited' postbox, where nobody seems to care about them.

If they are sent abroad, something might get wrong on Russian side as well.

You should just accept the fact, that in many countries the post is not fully reliable. Although most letters in Poland are delivered without problems, so you've simply got bad luck.

Or maybe the letter lies somewhere in sorting facility and someone will notice it in a few months... Wonder happens...

Honestly, when I get to post because I was noticed about registered package awaiting for me, and when I'm asked after 5 minutes of futile search, how big exactly is the package, I consider it a miracle that the letters are delivered at all...

You can't track mail if you don't have a tracking number (which is on the receipt in some cases, if there is a tracking number at all). There is a workaround:

Nowadays, in pretty much every country there is a service where you can print and send postcards you design online. If you send your vacation photo from Poland to Russia, you can use a Russian postcard printing service to send the card from Russia to Russia, with pictures from Poland while you are in Poland. These services often provide tracking, as well as reasonable estimates of delivery time.