As described in “Product Overview”, the Internationalization Module is built on the International Components for Unicode (ICU), the industry standard for Unicode processing. ICU is an open source library written in C and C++, and developed and maintained by IBM.

ICU constructs used by classes in the Internationalization Module are protected members of those classes. Should you need to access the underlying ICU constructs--to call obscure ICU methods, for example, or to interact with preexisting ICU code--you can do so by deriving from the appropriate class in the Internationalization Module. However, be aware that the non-public API may change without warning in future versions of the Internationalization Module.