Language Family Tree at Ethnologue.
This tree shows that there is a "Low Saxon" group of languages and in it you can find "Saxon, Low". This "Saxon, Low" is what the standard refers to as nds.
So let us analyse this mess a bit more. The Dutch Low Saxon languages are on a same level as nds which contain the German linguistic entities. This is the result of a different methods being applied to the Dutch and German "Low Saxon" languages.
In Germany there is a group fighting to preserve the "Saxon, Low" language. They do this by creating an overarching orthography for all the "Saxon, Low" linguistic entities. The idea is that as a result there are enough people to save the "Saxon, Low" language. In order to further their cause they have made this orthography mandatory. The problem is that they borrowed heavily from the German language. This resulted in the split of the nds.wikipedia.org; Dutch people who read and write "Low Saxon" found their language was no longer welcome.
There is a request for a so called "nds.wikisource.org". This is problematic on many levels. The nds code excludes the Dutch languages and there is no code for "Low Saxon". There COULD be a code for "Low Saxon", what is needed is to make a request to the maintainer of the ISO-639-5.
At this moment there is a request to rename the nds language in translatewiki.net into nds-de. You will now appreciate that this is technically not right. What would be right is leave the localisation alone and apply for a code for "Low Saxon". This would then be the correct code that is to be used with this new "Low Saxon" Wikisource.
When you think this is complicated, start thinking why this should not be part of the de.wikisource.org...