Hi @Stefan-Orvar-Sigmundsson, and thanks for this very thorough task!

Almost all (see comments below) of this is doable, but I'd like to see a community discussion on the Icelandic Wikipedia for the changes that affect it. Your reasoning makes sense, but it's still good to have the rest of the community on board. If you bring it up on the local village pump and there are no objections within a week, we can go through with the changes.

Special (-1): Sérstök means special as in special page. The current term, Kerfissíða, means System page. I do not know whence this term came but it is not a translation but rather an innovation. We should use the same term as the original.

I might be wrong, but I assume this translation was made by Ævar Arnfjörð Bjarmason, who was one of the early developers of MediaWiki. I like the term "System page" more than "Special" to be honest, because "Special" doesn't really tell much about what it is.

TímasetturTexti

Is this how you would write it in Icelandic, with CamelCase? The TimedText namespace is used for subtitles, so if you were to translate it at all, I would suggest using the Icelandic translation of "subtitle" instead.

There is an awkward situation with one of the namespaces. Namespace 106 which in the English project is named Rhymes is named Viðauki (Appendix) in the Icelandic project. It seems to me that when the Appendix namespace was added to the Icelandic project, it got the wrong namespace number. Either that or the English namespace number was changed later. I propose that the projects be brough into harmony in this respect. The simplest way would probably be to execute an SQL statement updating the page namespace value from 106 to 100 and then updating LocalSettings.php to reflect the change.

Custom namespace numbers (usually the ones starting from 100) actually have no inherent meaning, and while they may coincidentally correspond across different projects, it is not a problem that they don't. Attempting to change the namespace number would probably lead to lots of unforeseen complications, so that's a no-go. It is up to each project to decide which extra namespaces they want, and the order the number is assigned is usually the order they are requested in.

The projects that we have are small and often inactive for long periods.

Not true with Wikipedia and Wiktionary, but the rest, yes. Speaking of which, there has been NO discussion of this in the Icelandic projects. Agree with the required conseus.

I think that this namespace may have been named Image back in the day

It was indeed named Image back in the day.

TímasetturTextispjall

Should be "TímasettTextaspjall", or if spaces are allowed "Tímasett textaspjall".

Vísir

No, it is not representing a new thing, a sprout or anything like that. It is an numerical list.
So, it should be "Atriðaskrá" (subject) and "Atriðaskráarspjall" (talk) for the Index namespace.

Wikiorðabókspjall

No, you are going from an genitive case to a nominative case. Most of the other words (all but the TimedText translation) are in the genetive case, and this is not an exception. The current translation is correct. See https://bin.arnastofnun.is/leit/orðabók

Namespace 106 which in the English project is named Rhymes is named Viðauki (Appendix) in the Icelandic project.

This is a much larger problem than you can imagine and out of scope of this task.

The largest thing here would be having the current namespaces as aliases, especially in the Template and Module namespaces. This will create a massive mess otherwise, although it will only be for a while.

In T362441#9711103, @Snaevar wrote:

The largest thing here would be having the current namespaces as aliases, especially in the Template and Module namespaces. This will create a massive mess otherwise, although it will only be for a while.

Yes, we always do that when renaming namespaces.

I just did some Phabricator housekeeping and have no other involvement or opinion on this, or what level of consensus it needs.

I too sometimes wish things got done more and were subject to less arguing. But remember that Wikipedia is much bigger than it was back in Ævar Arnfjörð Bjarmason's days, so things inevitably happen slower.

In T362441#9711433, @Stefan-Orvar-Sigmundsson wrote:

Camel case is not how we write things normally, but this is just a technical approach since a literal translation here does not result in a compound noun but an adjective noun combination.

Answered your whole comment at https://is.wikipedia.org/wiki/Wikipedia:Potturinn#Íslenskar_þýðingar_nafnrýma, since Phabricator is not really a talking platform, although I know you think it is.