The Scandinavian Wikipedias are some of the most impressively developed, given the small number of native speakers of Swedish, Norwegian and Danish. These three wikipedias have 75,000, 31,000 and 25,000 articles respectively. But the situation with Norwegian is complicated by the fact that the language has two official written forms, Nynorsk (new Norwegian) and Bokmål (book language). This arises from the fact that Norway was ruled by Denmark for some four hundred years after the Kalmar Union in 1387, during which time Danish was the only widely used written language.
After Norway separated from Denmark and united with Sweden in 1814, movements to 'Norwegianise' the written language were started. One such movement, spearheaded by Knud Knudsen (whose Wikipedia biography in Nynorsk is three times as long as that in Bokmål), resulted in the development of a written standard called 'Riksmål', later Bokmål, retaining many similarities with Danish. A concurrent effort led by Ivar Aasen was more radical, and developed into modern Nynorsk. Today, all Norwegians know both forms of the written language, but about 90% of Norwegians use Bokmål as their first written language.
Now we can skip forward to 26 November 2001, when a Norwegian Wikipedia was created at http://no.wikipedia.org. Initially, this Wikipedia accepted articles in both forms of Norwegian, although given the prevalence of Bokmål there were very few Nynorsk articles. As the number of articles grew, particularly from late 2003 onwards, there were debates about how feasible it was to have two languages as distinct from each other as Swedish and Danish on the same Wikipedia. On 31 July 2004, a Nynorsk Wikipedia was founded and grew rapidly (it currently has over 7000 articles).
The success of Nynorsk led to renewed debates about the divisions between the two Wikipedias, with some on the original Norwegian Wikipedia feeling it should now become exclusively Bokmål, while others wanted to continue accepting all forms of Norwegian. The issue was put to a vote in March (see Wikipedia:Målform), revealing a slight majority in favour of a Bokmål-only Wikipedia. Notwithstanding this, the consensus was to leave the Wikipedia at the no. domain, rather than moving to the nb. that ISO 639-2 would suggest.
Given the strong feelings that could be aroused by a vote like this, the poll was overseen by two administrators from the Danish Wikipedia. This came about due to the Scandinavian Wikipedias' policy of coordination amongst themselves, via a page on the Meta-Wiki (Meta:Skanwiki). Because Swedish, Danish and Norwegian are all mutually comprehensible, articles written in one language can easily be understood by speakers of another. The Skanwiki initiative has led to the sharing of featured articles between the neighbouring Wikipedias, among other developments.
One sticking point for the new arrangement was that some Norwegian users proposed that there should now be a third Wikipedia, on which all forms of Norwegian would be acceptable. However, at the time of writing there seems to be a consensus among Nordic Wikipedians that this would lead to considerable duplication of effort.
The most visible effect of all this to users of the English Wikipedia is that where previously, interwiki links to Norwegian language articles took the form Norwegian and Norwegian (nynorsk), they are now styled Norwegian (bokmål) and Norwegian (nynorsk), to fully clarify the distinction between the two Norwegian Wikipedias.