> Foreign languages really become hard when they have features that do not appear in your own—things you never imagined you would have to learn. Which is another way of saying that languages slice up the messy reality of experience in strikingly different ways.
It does not follow that languages having different features results in "slicing up reality differently". That's only true if you believe some form of Sapir-Worf.
> Danish, for instance, does not have a word for “wood”; it just uses “tree” (trae).
Danish does have a word for wood...it's just the same as the word for tree. This is like saying English is weird because we say "he likes to fish" and "he eats fish" (or "he fishes" and "the fishes are swimming"). Fish is a noun and a verb, how weird! No, it's not weird at all, though it proves that context is important in understanding (no kidding).
> Russian splits blue into light (goluboi) and dark (sinii)
Great, and in English dark blue might be "navy".
All languages are easy to learn if you have to learn them. The people who think "Arabic and Chinese are hard" are people who don't have to learn them, they're doing it as a hobby or for school. If you're thrown into a situation where you need to acquire a language, odds are you'll figure it out.
This topic (differences between natural languages) always ends up as amateur sociology like "foreigners see things differently". It might be true but there's no evidence for it. Or all the evidence is baseless speculation that relies on assuming Sapir-Worf. To me, it all sounds like "inuits have 87 words for snow".