I have a sweater pattern that was translated from German. The finishing instructions say join sleeve seams, thereby sew together 8cm (approx. 3.1") of sleeve cuffs at lower end towards outside. I don’t know what this means. Is the lower part of cuff left open with the open seam edge finished somehow?
It sounds like the lower part of the sleeve is supposed to be turned back in the finished sweater to make a cuff. In order to seam it so the seam won’t show when you turn back the cuff, you seam the lower ~3" to the outside, then continue the seam up the sleeve on the inside of the sleeve.
You could seam the entire sleeve on the inside, but then you would have a seam showing when you turn back the cuff.