'Mannschaft' corresponds to 'mannskap' in Norwegian.

My dad had the complete set of Stewart Clark's Broken English books, and there's a ton of fun anecdotes like yours in those books, many of them based on Scandinavians' English mistakes. I should probably share a few of my favorites in a different thread.

My brother and I grew up speaking both English and Norwegian, and so we've had plenty of our own language mix-ups during the course of our lives: it took me embarrassingly long to realize that 'Kingdom of Norway' is 'Kongeriket Norge' and not 'Kongeriket av Norge' (age 13~14), that 'eventuelt' non est 'eventually' but rather 'possibly' (age 15~16) and that 'smal' non est 'small' but rather 'narrow' (age 20~21). My brother on the other hand pretty recently revealed that he still thought that 'sad' was an English-language synonym of 'semen' or 'sperm', by conflating it with Norwegian 'sæd' (which is actually cognate with 'seed'), and this is a mistake that I swear both of us made as kids, but which I evidently grew out of much faster.

My brother when he was a little kid also once said instead of "spider-like body", "eddercup-acty crap" (←edderkoppaktig kropp). What's interesting is that dialectal English does actually have the word 'attercop' for 'spider', and that Wiktionary asserts that 'crap' and 'kropp' actually are related. The semantic shift seems to be roughly like so: body → head of a plant → chaff → something discarded → poopydoodoo.