Have a look at this: en.wikipedia.org/wiki/Old_Norse .
In ArM5 it is customary to drop 'Old' prefixes before languages - though they are used by scholars. And Old East Norse and Old West Norse are just dialects of Old Norse, so need not be different languages in ArM5 at all. You can keep it simple and real, if your 13th century ArM5 Swede speaks Norse (Eastern) 5 and your Icelander Norse (Western) 5.
Cheers
GotF has Danish as a valid specialty of West Norse (p. 138).
For whatever that's worth.
The languages have only recently been splitting up enough to separate them. When investigating them a little while ago I had considered having East Norse, West Norse, and Gutnish be dialects of an Old Norse language, but ArM5 separated them further. You could alter this, but the way ArM5 has it, East Norse and West Norse are two different languages, each with several dialects. Dialects are at -1 to each other. So that would make Faroese , Greenlandic, Icelandic, Norn, and Norwegian all at -1 to each other. Similarly, Danish, Scanian, and Swedish would be at -1 to each other. Different but close languages are at -2 to each other. That would put East Norse and West Norse at -2 to each other, as well as to Gutnish.
As for other things, I have generally placed all the Old Norse languages the same distance from the other Germanic languages, at -3. The exceptions from/interpolated from the books:
And then there's one that was more guess-work than anything else because there is so little to go with:
I haven't gotten around to dealing with Pictish yet. Sorry.
That's an error. I pointed it out a while ago to David and it was confirmed, so it should be among the errata now.
This is because modern Norwegian is based more on East Norse (Danish to be more specific) than on West Norse after the Norwegian union with Denmark from the late 14th century onward. The traditional Norwegian based on West Norse is only spoken in rural dialects nowadays. A modern Scandinavian trying to understand a modern Icelander would be a more appropriate comparison.
Language barriers will be one of the main problems in this campaign. The two characters are quite unlikely to be from the same tribunal (Tytalus from the Rhine, Ex Misc probably from Stonehenge), and either way they'll end up in Iceland right at the start of the adventure and have to establish themselves there.
I've read that as well as several other articles. But in linguistics "dialects" are not necessarily what we commonly refer to, so I think splitting the abilities works well enough. The German Wikipedia goes into more detail on this, mentioning that from the 12th century onward the separation might actually be more like South Norse (Danish) and North Norse (Norwegian, Icelandic, Swedish) as Danish moved even further away. But I think gamewise the distinction works better as West and East Norse, anachronistic as that may be.
I mentioned this in my opening post - and thankfully it's in the errata, don't worry. 
Another language I noticed might become relevant: Gaelic (Highlands). How would that interact with the other languages? Haven't looked into the relations yet and have to leave the house soon. Any input on this is welcome.
Not even closely related as far as I know. There is information on Gaelic in The Contested Isle, which I have not yet put into my big chart for languages in and around Mythic Europe. I haven't had much chance to edit it since I posted it here a while ago: Languages in/around Mythic Europe
Just stumbled upon this little piece and had a chance to talk to a friend who's writing her dissertation on Icelandic sagas. According to her, there's a saga which tells that once upon a time Norsemen - that is Norwegians and Icelanders - and Englishmen were once able to understand each other, even though it seems doubtful to her. Still, if it's in a saga, it's good enough for Ars Magica.
So for the time being I think I'll treat it like this:
Gonna check out Gaelic later...
In the specific case of Old Norse, both historical sources and research, as referenced in the English and the German wiki, tend to call it a single language. For the more thorough German entry see de.wikipedia.org/wiki/Altnordische_Sprache :
It is your game and you decide, where to introduce complexities to it.
Cheers
Nice. I'll have to compare what I've written for ArM5 to that. At quick glance it looks like I have agreement. It seems odd that Greenlandic Norse is missing from that site, or did I just miss it?
That's why I'd originally placed it as one language, making dialects of East Norse, West Norse, and Gutnish. But the separation was happening right about the time of ArM5 sagas, and since the sagas move forward in time, that makes the separation grow during games instead of getting smaller. Thus the canon ArM5 separation is not unreasonable, either. For sake of consistency I split things as ArM5 canon does: East Norse, West Norse, and Gutnish being separate languages, not separate dialects.
Well, Snorri Sturluson is busy writing from 1220 or so, and he sees Norse as one language. So you would prepare your terminology for several decades ahead.
Cheers
I just looked around at the Funbo runes - thanks for that. Yes, the East Norse and West Norse do seem like just dialects of the same language, not very different at all. Of course, at a quick estimate this was 150 to 200 years prior to ArM5. That is consistent with other things I've read that they only started to become distinct enough to qualify them as different languages around the 13th century. So we're still stuck with a time where we could go either way. But a long-running ArM5 saga starting in 1220 would end up in the time when they're definitely separated as different languages. I suspect the ArM5 authors were looking at these options for East Norse vs. West Norse:
Cool. Didn't know about him.
However, I find the statement of "several decades" questionable. Snorri certainly didn't write for more than about two decades after the standard saga begins. Most of his life experience is from prior to when sagas begin, though right as sagas begin is a time when he was abroad. I would also note that he seemed to be mostly in Iceland or Norway, both of which would be West Norse - and ArM5 canon classifies Norwegian and Icelandic as the same language. I have to say I haven't read enough about him to know how familiar he was with East Norse or Gutnish to gain any more clarity, though.
So, as I've said. From what I'd read I was originally putting East Norse and West Norse together as dialects of Norse. But I switched to be consistent with ArM5 canon, and I still haven't seen anything that says ArM5 canon isn't the better of the two choices considering the time frame we're looking at (1220+ potentially many decades, maybe even to 1400 or later). Now, if you were playing a saga starting in 1120 instead of 1220, I would say you definitely want to go the direction of East Norse and West Norse being dialects of the same language.
The Heimskringla is (see p. 380 of Das Mittelalter in Daten, editor Joachim Heinzle, Munich, C. H. Beck 1993) dated around 1230. From the Heimskringla the quotes in the German wiki about a "danska tungu" (literally: Danish tongue) and "norrœnt mál" are taken. He is clearly a major witness, how knowledgeable speakers of the time felt about their language.
Cheers
That would be 1 decade, which is why I said I found "several decades" questionable.
Cool. So that establishes connection with Danish and thus East Norse (assuming the literal actually matches up with the translation). Does it say when he was there as a major witness?
Still, given the time frame involved for ArM5 sagas, I have yet to see anything saying the ArM5 canon choice is a poor one if a single choice is going to be made for simplicity for sagas running from 1220 to 1300 or maybe even 1400.
Don't forget that Snorri Thurlson is almost certainly related to Thord Thurlson (I am also adapting this campaign https://sites.google.com/site/aoidecovenant/) but I totally reskinned the beginning)
Bob
Thord Sturluson, elder brother of Snorri, is an NPC with Stats in LoF&I (p. 141f), and Snorri and the Sturlungar are also covered in the history section (p. 15ff) of that book. Snorri's work as a skald and historian (Prose Edda en.wikipedia.org/wiki/Heimskringla) is not mentioned in LoF&I however, and neither are his education and his excellent connections in Norway and Sweden.
Cheers
Yeah, I know about Contested Isle. Like I mentioned in the OP, it doesn't contain any information about relative modifiers though. Big shortcoming in my eyes, since this is one of the most important bits of information I'm looking for when I pick up a regional book.
So basically Gaelic speaking Scots and English speaking Englishmen couldn't understand each other at all? This might become relevant, as the old Vindolanda covenant site is situated on Hadrian's Wall.
Quite so. Unless one also spoke the language of the other 
.
For some real, complicated history of languages in medieval Scotland have a look at en.wikipedia.org/wiki/History_of ... s_language and the main articles it references (tmk no German version of these pages, sorry).
Btw, isn't the ArM4 Vindolanda at the Hadrian's Wall situated in Northumbria? In that case the people around it - on both sides of the wall - would speak the Northumbrian dialect of Old English. That's English (Northumbrian) in ArM5.
Cheers
As I understand, Gaelic and English are both Indo-European languages, and that's about how closely related they are.
English is more closely related to Latin - and during that periode, both languages would likely have been contaminated by the Norse languages spoken by the vikings. :-/