This plugin makes your permalinks as Cool IRI, even if your preferred language doesn't use US-ASCII.
The World Wide Web has been mainly constructed with US-ASCII, even for URL. But in now and future, WWW will shift from US-ASCII only world to Internationalized world with the help of Unicode, UTF-8, IRI, and so on.
If you are European, or Asian, or others, you would write an entry by your own language, therefore the title of it also will be with yours. However, the default MT removes or deforms non US-ASCII characters in title to make an entry basename for permalink URL(It is completely right in URI side). As a result, they couldn't enjoy full features of MT that can create Cool URI. Only English users could do.
Perl 5.8 Perl’s Encode module PHP’s mbstring extension if dynamic publishing in use.