ikke vs ingen? Is it similar to the German nicht vs kein in construction?
Ikke is "not"
Yes, it's the same.
How would you say 'that red house'?
It can be said same way, but you can say "det der røde hus" lit. that there red house if you need to be specific
ingen versus intet? What is the difference? Tak for dit svar.
"ingen" is for n-words and "intet" for t-words.
Why is "ingen" not plural? Is there no word like "inga" in swedish?
English is weird : No windows.
Does it mean not a single window ? Is zero plural ?
zero windows, one window, two windows ????
The number "zero" requires the noun to be in the plural. But this applies for many languages and is actually not weird.