Most useful language to learn between these?

From your list, I would say the one you would be most likely to find necessary on a visit to its country would be Russian. Good English is spoken so widely in the Netherlands, Sweden, Finland and Israel that it would almost ( I say 'almost') be a waste of time to learn those languages. But Russia is still in a state of flux, and while you'll meet English speakers everywhere in cities, you could easily find yourself in a part of the country where it's not spoken at all.

And once you've learned Russian, you're half way to being able to guess your way through Croat. I speak French, Russian and German, with reasonable reading ability in Italian and Spanish, very basic Turkish, a little Cantonese and a smattering of Estonian - which I did actually use on a short visit to Estonia a few years ago. Now of course everyone speaks English, but at the time they didn't, and they didn't want to hear me speak Russian either, not surprisingly.

Well I'm Scottish, English and Dutch, so I grew up learning Dutch from my father and I know it fluently so I recommend it as its fun to learn plus Holland is so nice, although the people there speak so much English you don't really spend much time speaking their language. I also speak Scottish Gaelic a little but not nearly as much as I do Dutch. I learnt French, Italian, Spanish and German through school and out of my own interest but my brother learnt Russian and Mandarin and he loved doing Russian, although he said it was really difficult.

He's trying to teach me them both and he also knows a little of Hebrew through his friend. So I would say either Russian or Dutch but probably Russian because if you get stuck there on your travels you can't rely on the locals to speak English like you can in Holland.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.