An Icelandic instrument - the langspil
General mountain dulcimer or music discussions
I suggest it is misleading to say that the Langspil is a "relative" of the dulcimer. The world has many three-stringed instruments which are plucked or bowed. I'm rather certain that many of them evolved independently.
People independently invent similar objects as solutions to a common problem. Would you say the heavy wooden hammer used to drive pegs for circus tents is a relative of a war club used by indigenous people in Tasmania? There are many conflicting patents for almost any device you can think of.
The Langspil is definitely descended from the Norwegian Langeleik. Iceland was "only a few days sail" from Norway back when both were part of Denmark's viking community.
https://en.wikipedia.org/wiki/Langspil
https://en.wikipedia.org/wiki/Langeleik
There is little evidence of overlap in Viking and Pennsylvania German communities in the 18th Century American colonies, although there were many inventive minds in both.
When you visit Iceland, you learn that in the early years ALL wood came from the sea (or was imported in longships.) As a result, they lived in some comfortable houses made from sod and burned peat.

It has a screen door handle on one side so it doesn't need a case