Here’s my translation

Alan

Einn dag veislunnar gengur meykóngur á dagþingan við sína fóstur-móður svo talandi: ‘Mér er sagt að fyrir eyju þeirri er Visio heitir ráði jarl sá er Virgilius heitir; hann er vitur og fjölkunnigur. 
One day of the-banquet [the] maiden-king goes to the-day-assembly (day-meeting) with her foster-mother so saying: “[It] is said to me that, over that island which is-called Visio rules (ráða fyrir e-u, Z16, McDonald doesn´t see this) that ‘earl’ who is called Virgilius; he is wise and skilled-in-magic.

Þessi ey liggur út undan Svíþjóð hinni köldu, út undir heimsskautið, þeirra landa er menn hafa spurn af. 
This island lies out beyond (lit: out from under) Sweden the cold (presumably referring to the colder northern part), out under (one of) the-(four) corner(s)-of-[the]-earth, (ie to the furthest earthly extent in that direction), of those lands which people have reports of (see also heims-skaut, CV, ‘pole’, but this seems to me a more Modern meaning).

Í þessari eyju er vatn eitt stórt, en í vatninu er hólmi sá er Skóga-blómi heitir og svo er mér sagt að hvergi í heiminum megi finnast náttúrusteinar, epli, og læknis-grös fleiri en þar. 
In this island is a certain large lake, but (and) in the lake is that islet which is-called Skóga-blómi (Forests’-Bloom) and so [it] is said to me that nowhere in the world (ie on earth) more than there may be-found stones-possessing-special-virtues, apples (or tree-fruits, in general), and medicinal (healing) herbs.

Nú vil ég halda þangað einn skipa og son þinn Hléskjöldur með mér’. 
Now I want to steer thither in a certain ship (Can´t figure out the grammar here, <einn> appears masc acc sg while <skipa> appears neut gen pl. Is there a wk masc noun <skipi> ?)  and your son Hléskjöldr with me.

Drottning Egidía talaði tormerki á ferðinni, og þótti háskaleg. 
Queen Egidía raised difficulties about the-journey, and [it] was-reckoned dangerous.

Meykóngur varð þó að ráða, býst Hléskjöldur nú í ferð þeirra og sigla með heiður út af Pul fagurt byrleiði. 
[The] maiden-king nevertheless had (was obliged) (<verða at> + inf) to decide (or ‘have her way’, Z6, Z9), Hléskjöldr prepares-himself now [to go] on their journey and [they] sail with honour out from Púll (Apulia) with fair favourable-winds.

Hef ég ei heyrt sagt frá þeirra ferð né farlengd fyrr en þau taka eyna Visio. 
I have not heard said about their journey nor (the extent of) travels before they reached the-island Visio.

Einn dag, leggjandi skipið í einn leynivog, ganga síðan upp um eyna þar til er þau finna vatnið. 
One day, steering the-ship (probably accusative) into a certain hidden-bay (leyni + vágr, Z2), [they] go [on foot] after-that up across the-island until they find the-lake.

Þau sjá einn bát fljótandi, taka hann og róa út í hólminn. 
They see a certain boat floating, take it (<bát> is masc so acc pron. agrees with it) and row out to the-islet.

Þar voru margar eikur með fagri fruckt og ágætum eplum. 
There were many oaks (or trees in general) with fine fruit and excellent apples (or tree-fruits in general).

Sem þau fram koma í miðjan hólman sjá þau eitt steinker með fjórum hornum. 
As they come forward to [the] middle [of] the-islet they see a certain stone-vessel with four corners (drinking-horns?)

Kerið var fullt af vatni; sinn steinn var í hverju horni kersins. 
The-vessel was full of water; in each corner of the-vessel was its (respective) stone (<sinn>, Z5, presumably <steinn> here is not the subject of the sentence).

Meykóngur leit í steinana; hún sá þá um allar hálfar veraldarinnar, þar með kónga og kónga sonu og hvað hver hafðist að, og allar þjóðir hvers lands og margar ýmislegar skepnur og óþjóðir. 
[The] maiden-king looked into the-stones; she saw then around all regions of the-world, there with kings and sons of kings and what each did, and all peoples of each land and many diverse creatures and evil-beings (lit: un-people).

Drottning  gladdist nú við þessa sýn, takandi kerið og alla þessa steina, epli, og læknis-grös, því að hún undirstóð af sinni visku hverja náttúru hver bar. 
[The] queen was-gladdened by this-vision, taking the-vessel and all these stones, apples (or, tree-fruits in general), and medicinal-herbs, because she understood from her (<sinn> poss pron refl) wisdom, (<viska>, MnI) what nature (ie special virtues, magical powers) each bore.

Skundar nú sínum veg aftur til skips síns, siglandi burt af Visio hvað þau máttu. 
[She] hastens now her way back to her ship, sailing away from Visio by what [means], (ie however) they could.

Nú er að segja að jarlinn verður vís hverju hann er ræntur. 
Now [one] is to say that the-‘earl’ became aware (informed) of what (or how) he is (ie has been) plundered.

Má þar sjá mart skip siglandi og róandi eftir þeim. 
[One] may see a many a ship (note: gramm sg) sailing and rowing after them.

Sjá nú hvorir aðra. 
Each-of-the-two (parties) now sees the-other.