Problems with iconv on macOS

For conversion of strings from a given character encoding to another, R uses iconv, a function defined by POSIX. It is available on Linux and macOS with the operating system and for Windows, R ships with a slightly customized version of win_iconv, which implements the same functionality on top of Windows API. The differences between iconv implementations, partially allowed by a rather permissive definition of the interface in POSIX, pose a challenge for maintaining R and cause differences between platforms observed by users.