editline/docs/LOCALE.md

Locale Considerations

The editline library has basic support for locales via the use of the standard POSIX functions mbrtowc and wcwidth. As a result, the on-screen width of characters in printed text should be calculated correctly, the so-called East Asian ambiguous characters being a notable exception.

The input handling is not yet multibyte-aware. Specifically, the presence of non-self-synchonizing encodings requires always segmenting the whole string using mbrlen when deleting.

Programs wishing to use the feature need to link to a build of editline configured with --enable-locale. In addition, the program should call setlocale(LC_CTYPE, "") to use the locale settings of the environment.