Boost.Locale allows you to work safely with multiple locales in the same process. As we mentioned before, the locale generation process is not a cheap one. Thus, when we work with multiple locales and need to switch between them, we recommend that you create all the locales you need when the program starts.

To simplify this process, the boost::locale::generator class has an option to cache all generated locales. With this option, when you create a locale that was previously generated, it would be fetched from the existing locale set instead. This operation is thread safe.

This option must be explicitly enabled by calling the locale_cache_enabled member function of boost::locale::generator with true as the parameter.

For example:

generator gen;
gen.locale_cache_enabled(true);
gen("en_US.UTF-8");
gen("de_DE.UTF-8");
gen("ja_JP.UTF-8");
// Create all locales
std::locale en=gen("en_US.UTF-8"); 
// Fetch an existing locale from the cache
std::locale ar=gen("ar_EG.UTF-8");
// Because ar_EG not in the cache, a new locale is generated (and cached)

Then these locales can be imbued to iostreams or used directly as parameters to various functions.