&reftitle.install; mbstring is a non-default extension. This means it is not enabled by default. You must explicitly enable the module with the configure option. See the Install section for details. The following configure options are related to the mbstring module. --enable-mbstring=LANG: Enable mbstring functions. This option is required to use mbstring functions. As of PHP 4.3.0, mbstring extension provides enhanced support for Simplified Chinese, Traditional Chinese, Korean, and Russian in addition to Japanese. To enable that feature, you will have to supply either one of the following options to the LANG parameter; --enable-mbstring=cn for Simplified Chinese support, --enable-mbstring=tw for Traditional Chinese support, --enable-mbstring=kr for Korean support, --enable-mbstring=ru for Russian support, and --enable-mbstring=ja for Japanese support. Also --enable-mbstring=all is convenient for you to enable all the supported languages listed above. Japanese language support is also enabled by --enable-mbstring without any options for the sake of backwards compatibility. --enable-mbstr-enc-trans : Enable HTTP input character encoding conversion using mbstring conversion engine. If this feature is enabled, HTTP input character encoding may be converted to mbstring.internal_encoding automatically. As of PHP 4.3.0, the option --enable-mbstr-enc-trans was eliminated and replaced with the runtime setting mbstring.encoding_translation. HTTP input character encoding conversion is enabled when this is set to On (the default is Off). --enable-mbregex: Enable regular expression functions with multibyte character support.