Highly advisable that travelers should check this site out before venturing into the highlands.

The “ll” sound my even sound more like “ddl”… Also the “ll” sound can be different, for instance the name “Gulli” (short for f.e. Guðlaugur) is said differently than “Bolli” (a name and also the Icelandic for a cup)… Bolli has the “ddl” sound to it but Gulli has the “ll” sound as in yellow…. but when to use wich?
Can´t tell you, I don´t think there´s a rule about it.

Some tips on traveling around Iceland:
There are a few things to keep in mind when traveling in Iceland, especially the highlands and even more especially going on glaciers, it can be very very dangerous. So having a Gps that gives coordinates and leaving a travel plan with someone (if you can) can save your life, and not venture somewhere without talking to the locals. Alot of them know what to be aware of. 3 little examples:

I remember one man (1 or 2 years ago) who went (if I remember correctly) walking on Eyjafjallajökull and fell into a crevasse. He survived the fall, and had a signal on his cell phone so he called for help. He told them he had fallen in a crevasse in Eyjafjallajökull and needed help. Search and rescue went there to search for him, and they are highly trained in these circumstances (and all of them are volunteers) but didn´t find him. He was found though a few days later. He had read the map wrong and went walking on a wrong glacier wich is full of cracks. He never stood a chance to poor guy.

A couple from Canada went to the Highlands to see the rough nature of Iceland, (this was this fall/early winter). They were driving in nice weather and enjoying the country. A snow storm hit suddenly and fortunately they saw an emergency shelter wich they stopped their car by. They were found one week later alive and well, but nobody knew that they were there. A guy was driving from shelter to shelter just to check if there might be someone there, and well, they were really lucky.

I went hunting ptarmigan in the highlands with my brother. Out first ptarmigan hunting trip.
We went early morning, 5 am and came down from the mountain at around 5 pm. Hard walk that :) Tried to start the car but nothing. The starter motor had ceased working. The cell phones had no connection so we couldn´t let anyone know we had problems.
The temp. was -15°C (I think that´s 5°F) and the wind was very strong, so the wind chill was crazy. We stayed in the car from 5 pm till 2:30 am, until rescue came. Fortunately by dumb luck, my brother had left a travel plan for his wife so it didn´t take so much time to find us. But man we were cold when they got there. We never go hunting after that without leaving a travel plan and a time when we should contact.

This is just to keep in mind :)