No, I think you're somewhat missing what is meant by "untranslatable" - the idea behind it is that there are many singular words in other languages which immediately bring about a specific idea or evoke specific emotions or thoughts, etc. It's not that the word can't be explained in English, it's that there isn't an English equivalent of a word, and often they even lack phrases.

Defining the word isn't really the same, since that's English assimilating the word, not translating it. A very simple and classic example is bouquet; a literal translation would be closer to a small collection of plants (not even flowers necessarily, I think it's something like "little wood"); however, if you said "bouquet" in French, it was understood that you weren't talking about bushes or trees, it was specifically a pretty grouping of flowers. Subsequently, when the word gets to English speakers, they don't have a word for it really - a bunch of flowers is just "a bunch of flowers". There's a bush, there's a grove, there's a bundle, and so on, but when you want to talk about a pretty arrangement of flowers, you use bouquet.

But don't mistake assimilation for translating the word, it's just defining it. Look at the list the author compiled on their site:

http://media.wix.com/ugd/ce8de8_70080eab413e468580b0fc37b59d...

Just go and pick some of the words and try to define them as concisely as you can with one English word, or even an idiom/slang/phrase. Some maybe, but most don't really have any simple equivalent or similarity in English. Even with the definition of some of them, quite a few would be hard to use correctly in an English sentence.

Like, consider a few of the russian words:

тоска) (Russian, n.): longing for one’s homeland, with nostalgia and wistfulness.

I think we could call that homesickness, cultural rejection, or a few other English words that are similar (though from the Russians I know that are versed in English, they disagree and say homesick misses how deep of a feeling тоска has.

But then consider авось: (Russian, particle): maybe/what if; faith/trust/hope in luck, serendipity, destiny or fate.

What English particle would convey the same idea here? Better yet, how would you convey such a concept in English with any other word combination?

This is why assimilation comes into play and why translations aren't always reliable. Languages can be vastly different, even if they're categorized the same. Slavic languages rarely (if ever) use "to be" in most of its tenses, and as such, they construct descriptions and ideas far differently than you would in the Germanic based languages - as the languages evolved with different rules, naturally certain words were necessary for either standard communication or for artistic license, words which were not necessary in other languages simply because they didn't evolve that way. Assimilation plays an important part in language even today: Say the English word "Coffee" at a restaurant just about anywhere in the world and odds are you will get a cup of coffee. Say "Computer" or "Phone", and likely they'll know what you mean. But again, that's assimilation - where there was no word, but there was a need, the word was taken. The truth is there are many words in many languages that as English speakers we don't know if we need; the words are foreign to how we think and write and speak.