Hi.
The Polish language has some great proverbs. I tried to find some information about the one you mentioned.
https://en.wiktionary.org/wiki/g%C3%B3ra_z_g%C3%B3r%C4%85_si%C4%99_nie_zejdzie,_a_cz%C5%82owiek_z_cz%C5%82owiekiem_zawsze shows the meaning as:
one can find someone known in unexpecting (should be �unexpected�) places or times
https://moscsp.ru/en/polskaya-poslovica-na-russkii-yazyk-perevoditsya-kak-polskie-poslovicy.html
Mountain does not converge with mountain, but man and man will converge.
The Dictionary of European Proverbs by Emanuel Strauss includes this:
men may meet sooner than mountains
I don�t know of any English proverb that has that exact meaning and I agree with what you said; the translations do not sound authentic. The idioms that you mentioned do seem close to it in meaning. �Cross someone�s path�, �happen along�, �bump into someone� and �run into someone� are also similar.
I hope that helps!