@linusdm, sorry for you not having much fun with this. The documentation definitely needs improvement in this area - my lack of knowledge of the various Linux denominations if the primary fault. I hope others more experienced than I am (probably everyone!) can chime in.
My reading suggests that installing the package icu should bring in the right versions of libicu-dev and libicu for whatever version of Debian you are on.
BTW, I’ve only recently become aware that while Ubuntu and MacOS come with libicu installed (the runtime requirement), Debian and Alpine do not. Which is why runtime requirements haven’t been mentioned - I will fix that now I have some more knowledge (albeit not enough!).
Please do open an issue so we can get to the bottom of this ASAP.
