"Multilingual" computing can mean:
Multilanguage--multiple launches of one locale, one script.
Multiscript--single launch of one locale, multiple scripts.
Multilingual--single launch of multiple locales, multiple scripts.
The movement from multilanguage to multiscript to multilingual implies an increased level of complexity in the underlying operating environment.
In a multilanguage environment, a locale supports one script and one set of cultural attributes. An application inherits all the language and cultural attributes of the current locale. Document text is written in one script and text manipulated according to the locale language rules. A separate application launch in another locale is required to use different language and cultural attributes.
For example, to write a document in Chinese, a user first sets the Chinese locale before launching the application. To write a Russian document, the Russian locale must be separately set and the application launched again. Chinese and Russian text cannot be mixed in the same document
In a multiscript environment, a locale can support more than one script, but only one locale can be set as current. An application creates a document in different scripts by tagging each separate script run (text in the same script). However, the current locale environment settings apply--for example, text is sorted according to the sorting rules of the current locale.
In the Chinese/Russian example above, rather than create two separate documents, the user creates one multiscript document containing both Chinese and Russian text. The cultural attributes of the active locale still apply--in the Chinese locale, the Chinese sorting rules apply to the mixed-script text.
In a Unicode locale, tagging script runs is not necessary because all language attributes are inherent in the Unicode codeset.
In a multilingual environment, a locale can support multiple scripts and multiple cultural attributes, giving an application greater control over text manipulation. For example, a document containing text in multiple scripts can sort text according to the sort order of each script rather than the current locale.
In the Chinese/Russian example above, the Chinese locale sorting rules apply to the Chinese text and the Russian sorting rules apply to the Russian text.
The multilingual environment is closest to the ideal of multilingual computing. An application uses locale data from numerous locales, while at the same time allowing easy text manipulation in a variety of scripts. All users can easily work in their own language and be understood by others around the world.