"Where is snow?"
Translation:Hol van hó?
The English for this sentence doesn't even make sense? Who ever says 'Where is snow?'
Agreed. Even if, say, you took a trip to Alaska only to find that all the snow had mysteriously vanished, we'd at least use an article: "Where's the snow?" Unless they're just asking where snow is generally found, but even then it probably be worded like "Where is there snow?".
The Hungarian sentence conveys the latter meaning. "Where is there snow?" would be the correct translation.
Why does the word "hó" have not a standart plural form "havak"? According to vowel garmony it have to be "hók".
I think the original word had a -v- in it (perhaps something like "hav") which survived in the plural ("havak") but in the singular, "hav" turned into "hó" as the final consonant merged with the vowel.
Similar with e.g. kő "stone", plural "kövek" or ló "horse", plural "lovak" where a final -v disappeared in the singular but remained in the other forms.
Greek has similar things as well, e.g. -ματ turned into -μα which is why we have "enigma" but "enigmatic" or "stigma" but "stigmata"; and Slavic has this e.g. in nouns for young animals where a final -t was dropped in the base form but kept in the forms with endings, e.g. Ukrainian теля "calf" but plural телята.