Tronic2

The decoding phase will do that, if needed. Also note that in many cases you must process it as opaque binary, even though it should be valid UTF-8. This is in particular with filenames on POSIX systems because otherwise you could not access any files that happen to have invalid UTF-8 in their names.

Ignore all character support in the standard library and handle UTF-8 as opaque binary buffers. If you need complex string algorithms, decode into UCS-4 (UTF-32). You'll find short encoding and decoding functions on StackOverflow. For case-insensitive comparisons and sorting, use an external library that knows the latest Unicode standard.

Syntax of pointers. Easy to use high level languages make extensive use of pointers (i.e. all their variables are actually pointers) but beginners cope with them because no stars or ampersands are required, with the help of GC. Of course they'll get bitten soon and often because it is too easy to create copies of pointers rather than copies of full data structures, and without understanding pointers it's hard to grasp why that happens.

char effectively behaves as a signed type, making it unsuitable for binary operations (e.g. UTF-8 manipulation). I/O functions deal with char pointers, so using unsigned type like uint8_t requires casting back and forth. Is there any way out of this problem, and am I already breaking the aliasing rules with that cast?

Why is the struct tm* returned by localtime() not thread-local like errno and other similar variables are (at least in implementations)? Do you have any plans to improve calendar support for practical uses?