Accessing ICU from CocoaEdit
Apple ships ICU with Mac OS X but only as a private library with no headers. You could try building ICU yourself and embedding it in your application but the library is huge (about 8 megabytes) due to the size of the conversion tables and other data it contains (see http://icu-project.org/userguide/icudata.html#custom_data_library).
Until Apple decides to make the API public, one sneaky way of using it indirectly without having to meddle with private libraries is to access it via NSPredicate.