|>> || Polish is Slavic. It's like Czech, Slovak, or Sorbian, or to a far different degree, sorta like Russian, Ukrainian, Belorussian, or even Macedonian, Bulgarian, or the things that Serbian is a part of. It's also maybe the hardest of all the Slavic languages to learn, in part because it's highly "conservative" (it's more basal and keeps a lot of the defining irregularities of the other Slavic languages). |
Dutch is like halfway between Modern German and Old English - not Early Modern English of the Bible or Middle English of Chaucer but the old English of Beowulf (ie HWAET we Gar-dena, in gear-dagum, theod-cyninga þrym gefrunon...).
But its MUCH more like Modern German than either; Dutch is almost mutually intelligible with German, which is to say they can almost be understood by each other without the other really learning anything about them. Dutch is also kinda Frenchy - it's usually nasally and has more French words that German. It insists even harder than German on the uvular Parisian r.
Dutch also kinda buys you Afrikaans if you ever want to go to former Dutch Africa.
Danish is North Germanic - it's completely unintelligible from the rest, but German has areas where it gradually becomes Danish like it does with Dutch. But the language is relatively very different from German. It's benefit to English is English has a bunch (but not a whole lot) of words borrowed from what you can call the immediate ancestor of Danish, Swedish, and Icelandic.
Danish buys you about half of Norway, the standard languages being close enough in writing and speaking that they usually get treated as one language by companies. It kinda buys you the less standard Norwegian and maybe Swedish too, in the same way German buys you most of Dutch. Note that there's still a lot of differences, it's not like you just get it for free.
Polish has limited use, but businesses like it because Poland got the economic shock after the collapse of the Polish People's Republic. But I say again it hard.
Dutch has arguably the most use and is close enough to German that it's more like learning the differences between it and German than learning a whole nother language. It isn't as useful business wise, though working Benelux (Dutch+Belgian French) things is growing more viable. It's also mildly useful if you intend to ever try and work in some of the former Dutch African countries, like Namibia, South Africa, Botswana, Zimbabwe (fat chance), or to a much much lesser extent Angola. Indonesia has some work for it too, being that they're the former Dutch Indies. But pretty much the only things you could there they all have more than enough of, or are wholly academic like documenting Khoe-San languages.
Danish really doesn't have a use outside of Denmark, Norway, and to a lesser extent Sweden. Probably the least useful of the three. But you know Hans Christian Anderson.