so what's with the "the" in the hungarian original? is it necessary? Because "I like the girls is wrong, I believe.
Yes, it's necessary. Both "I like girls" (referring to girls in general) and "I like the girls" (referring to a specific group of girls) are translated as "Szeretem a lányokat."
Can there be any context/use for Szeretem egy lanyokat?
That's not a correct sentence; the indefinite article can never be followed by a plural noun (just like how you wouldn't say "a girls" in English).
Could you say "szeretek néhány lányokat", meaning "I like some girls"?
"Néhány", just like all other numerals in Hungarian, takes a singular noun, so you would have to say "Szeretek néhány lányt."
Oops, true, I forgot. Thanks!
I belive in that case you would also have to use the indefinite, i.e."Szeretek egy lányt".