In this sentence, svona means something like so, like that, or this way, depending on how naturally you want to translate it.
With lágt, it gives the idea of degree:
It is pointing to the manner or level of the whispering.
Yes. Lágt comes from lágur = low.
But when talking about sound or volume, Icelandic uses lágt the way English might use:
So hvísla svona lágt is not about physical height. It means whispering at a very low volume.
Also, Icelandic often uses the neuter singular form of an adjective as an adverb, and that is what is happening here.
Yes, hvísla already means to whisper, so quietness is already built in.
Adding svona lágt gives extra emphasis. It means something like:
So the speaker is not just objecting to whispering in general, but to whispering at such a low volume that they cannot hear well.
Heyri is the 1st person singular present tense of að heyra = to hear.
So:
In context, English often says I can hear, but Icelandic frequently just uses heyra where English prefers can hear.
So ég heyri þig ekki vel naturally means I don’t hear you well or I can’t hear you well.
Because þig is the object form of you.
Icelandic marks this difference clearly, unlike modern English.
So:
This is normal Icelandic main-clause word order.
A simple way to think about it is:
Icelandic usually puts the finite verb early in the clause, and short object pronouns like þig often come before ekki.
So ég heyri þig ekki vel is a very natural order.
Because each clause is negated separately.
So this is not a double negative in one clause. It is just one ekki for each part of the sentence.
Not exactly.
These can be close, but ekki vel is often softer and more neutral. It simply says the hearing is not good enough. Illa can sound a bit stronger or more direct.
So in this sentence, ég heyri þig ekki vel is a very natural way to say that the speaker cannot hear the other person properly.