> Það er sagt einhverja nótt að meyna Herdísi dreymdi að
> kona kæmi að henni.

> It is said each night that maiden Herdis dreamt that a
> woman came to her.

> It is said some night that (the) girl, Herdis, dreamed
> that a woman came to her.

> That is said that one night (it) was-dreamed by maidenly
> (young?) Herdís that a woman came to her.

Noun <mey> plus article in the fem. acc. sing.; the subject
of <dreyma> is typically in the accusative, and *meyina
contracts to <meyna>.

> Ekki sýndist henni konan svipleg.

> It didn’t seem to her the woman had a displeasing air. (Z.
> glosses this sentence under “svipligr.”)

> She didn’t seem unhappy.

> The-woman did not-seem to her (as) having-a-displeased-air
> (svipligr, Z2)

Either Zoëga meant ‘having a displeased air’ to apply to the
whole phrase <ekki sýndist henni konan svipligr>, or he’s
out of line with all of the other sources that I checked.
The relevant gloss in CV is 'sightly', so that <ekki
sviplig> here is 'unsightly'; Baetke has 'von angenehmem
Aussehen (?)' ('of pleasant appearance (?)'); the notes to
another edition gloss it „von gefälligem aussehen“, which is
essentially the same thing; and MM&HP clearly interpret it
that way as well (‘thought she looked very unpleasant’).
This also fits the rest of the passage better.

> En þó mundi eg við þig semja ef mér þætti eigi meiri bóta
> vant þar sem Guðrún er.”

> And yet I would treat with you if it didn’t seem to me
> more a troublesome cure there where Gudrun is.”

> But still I would agree with you if to me did not seem
> more ? lacking there where Gudrun is.”

> But nevertheless I would treat (get along, semja, Z2) with
> you if (it) seemed to me not a wanting of greater remedies
> (cures, bót, Z1) where Guðrún is (ie  if there weren´t so
> many problems as far as Guðrún is concerned).”

<Vant> is the adjective <vanr> 'lacking, wanting', which
takes the genitive (here gen. plur. <bóta>) of the thing
that is lacking: ‘if [it] did not seem to me lacking in more
“betterings” there where Guðrún is’.

> Um morguninn eftir lét Guðrún taka upp fjalar úr
> kirkjugólfinu þar sem hún var vön að falla á knébeð.

> During the next morning, Gudrun had boards taken out of
> the church floor, there were she was accustomed to kneel.

> During the next morning Gudrun had boards taken up from
> the church floor there where she was accustomed to fall on
> a knee cushion.

> The next morning after, Guðrún caused to take up planks
> (boards, fjöl) out-of the-church-floor where she was
> accustomed to fall on (her) knee-bed /bolster, cushion).

According to Zoëga, <falla á knébeð> is mildly idiomatic,
being simply 'to kneel'.

> Þau voru blá og illileg.

> They were black and hideous. (“blá” can mean either blue
> or black, and I thought “black” fit better)

> They were black and hideous.

> They were blue (black) and ill-looking.  

I’m inclined to interpret <blá> here as 'livid,
black-and-blue'.

> Þar fannst og kinga og seiðstafur mikill.

> There were also found a brooch and a large enchanter’s
> wand. (Good vocabulary for when I decide to read Harry
> Potter in Old Icelandic J)

It seems that you can at least read it in the modern
language:

Harry Potter og viskusteinninn
Harry Potter og leyniklefinn
Harry Potter og fanginn frá Azkaban
Harry Potter og eldbikarinn
Harry Potter og Fönixreglan
Harry Potter og blendingsprinsinn
Harry Potter og dauðadjásnin

> Hann var kallaður Bolli hinn prúði.
> He was called Bolli the showy.
> He was called Bolli the powerful.
> He was called Bolli the Magnificient (Showy?).

Baetke makes it 'auf sein Ansehen bedacht, großartig
auftretend; stattlich, prächtig' ('concerned about or
careful of his appearance, magnificent appearing; handsome,
impressive, stately, magnificent'). 'Showy' sounds good
here.

Brian