I would probably want to learn something of the language
Of course! That's part of it. But it is impossible to learn the language of every country you work in if you work here and there. However, I do my best to use the little Polish i know in every day life.
in order to derive some lasting benefit from the experience.
You see, I do not know if I am here for the long-haul. I am in Poland now. Maybe for one more year, maybe two, maybe three maybe for the rest of my live. I do not know how long my Poland stay will last for. But if i ever realize that my stay here will be longer than my working contract indicates, i might put in an extra effort to learn the language properly. Until then, I get by with what I know and still enjoy being part of society as much as the Polish people, who welcome me into their midst, enjoy to speak English to me while teaching me a bit more Polish.
If your partner speaks no German (or even little English) and you even less Polish
Why would you assume that every foreigner going to Poland goes to Poland for a girl? There are plenty of other reasons to move to Poland.
But, when i lived in Holland i dated a Scottish girl. For the first three weeks I didn't have a clue what she was saying to me. Perhaps that was the reason why we got on so well. She could talk and I would just be a good listener........