The Need to Compare CS Extension
Trouble is that still leaves out much of the world. For example, to support Eastern European languages you need to use a different character set, often referred to as Latin 2, which provides the characters that are uniquely needed for these languages. There are also separate character sets for Baltic languages, Turkish, Arabic, Hebrew, and on and on. When having to internationalize software for the first time, sometimes companies will start with just supporting ISO Latin 1 if it meets their immediate marketing requirements and deal with the more extensive work of supporting other languages later. The reason is that it's likely these software applications will need major reworking of the encoding support in their database and functions, methods and classes within their source code to go beyond ISO Latin support, which means more time and more money - often cascading into later releases and foregone revenues. However, if the software company has truly global ambitions, they will need to take that plunge and provide Unicode support. I'll argue that if companies are supporting global customers, and even not doing a bit of translation/localization for the interface, they still need to support Unicode so they can provide processing of their customer's global data.
We come back to Unicode, which as we mentioned above, is a character set created to enable support of any written language worldwide. Now you might find a language or two lacking Unicode support for its script but that is becoming extremely isolated. For instance, currently Javanese, Loma, and Tai Viet are among scripts not yet supported. Arcane until you need them I suppose. I remember a few years ago when we were developing a multi-lingual site which needed support for Khmer and Armenian, and we were thankful that Unicode had just added their support a few months prior. If you have a marketing requirement for your software to support Japanese or Chinese, think Unicode. That's because you will need to move to a double-byte encoding at the very least, and as soon as you go through the trouble to do that, you might as well support Unicode and get the added benefit of support for all languages.