Problems linking ICU UText, undefined reference
It is worth knowing that libicu likes to append version strings to its API symbols behind your back. If your header files do not match your libraries, like say you have the Swift compiler installed on Debian and it has replaced /usr/include/unicode/ with its own nailed down version, then you try to link symbols like utext_close_swift_65 or similar and you will be unhappy.
I removed the swift compiler and reinstalled the libicu-dev package and all is good now.