"Let's drink a bottle of wine together."
Translation:Vypijme spolu láhev vína.
It is not an easy question. Seemingly, even to a native speaker, those two words are identical. Yet, sitting here trying to come up with sentences, it turns out that we use SPOLU when we are engaging in the activity at the same time, side by side. My dirty mind comes up with SPÍME SPOLU - we are sleeping together, which suggests romantic relationship, while SPÍME DOHROMADY suggests we share a room but nothing else. If we drank the wine DOHROMADY we might simply each drink half of it but not at the same time at the same place.