> While half of the language design of C is questionable and outright dangerous, making its functions locale-sensitive by all popular OSes was an avoidable mistake. Yet everybody did that. Just the existence of this behavior is a reason I would like to get rid of anything GNU-based in the systems I develop today.

POSIX requires that many functions account for the current locale. I'm not sure why you are blaming GNU for this.

C wasn't designed to be running facebook, it was designed to not have to write assembly.

I'm not sure why you are blaming POSIX! The role of POSIX is to write down what is already common practice in almost all POSIX-like systems. It doesn't usually specify new behaviour.