Birte does her fibre extraction from dried nettle stems. It works, but........well in the past they were retted like flax. It stinks though, then stooked and dried and then they were broken and scutched. Then the bundles are combed to free the fibres from the broken stems. It's hard work but it makes for enough fibres, of good quality, that are fit for spinning to make thread worth weaving.
There is another way, perhaps more appropriate to bushcraft, that I find useful.
The stems are stripped before they get too dry, and then those lengths are simmered in a mild alkali for a couple of hours. Then worked a bit and finally combed.
The result is handfuls of fine white fibres, ready to be spun worsted style (fibres all running the one way, not fluffed as though for knitting wool) into fine thread.
That fine thread makes a beautiful weaving cloth
The first stage of the process, as the stuff comes out of the simmering pot, can be used to make cordage without anymore work, and it's good cordage too. Very supple, handleable, strong and hardwearing.
All of these ways work, but the labour is different in each case, and the results, the final products, are in some ways dependant on the preparation processes.
cheers,
Toddy