Extended Characters Locales and Extended Characters A computer system can support more than one multibyte character code, and more than one wide character code. Each locale specifies a particular multibyte character code and a particular wide character code. The choice of locale influences the behavior of the conversion functions in the library.
Some locales support neither wide characters nor nontrivial multibyte characters.
In these locales, the library conversion functions still work, even though what they do is basically trivial. If you select a new locale for character classification, the internal shift state maintained by these functions can become confused, so it's not a good idea to change the locale while you are in the middle of processing a string.