Very early versions of LANSA had basic national language support for all languages (other than bi-directional and IGC/DBCS languages).
This meant that it was relatively easy to set up a LANSA application to run exclusively in, for example, Swedish.
However, that's all the application could do, run in Swedish.
With full multilingual support it is possible to create an application so that at execution time you can elect to run the application in any of your supported application languages. For example you may have defined your application to run Swedish, French, Italian, German or English.
In fact, two users of the same program can sit side by side, with one running the application in French and the other in Italian.
In summary, a national language application can "speak" in one language, a multilingual application can "speak" in many different languages.