In a european environment it sometimes happens that one wants to write a document that contains more than one language. I have an example of a document, published by the EEC, that contains 9 (nine) different languages. Also in linguistics one can find documents written in more than one language, i.e. to compare two languages.
If you have to write such a multilingual document you should try to conform to the typographical conventions in use for each language. A well known example is the type of quotation marks used. TEX supplies the user with ``quoted text'', but a Dutch user might want to have @=, @=''@=@ @-@ @=@@@=@ @=@ @quoted text'', whereas a German text should contain glqqquoted textgrqq and a frenchman would perhaps like to see something like flqqquoted textfrqq. These language specific conventions should be implemented in a document-style option file for each language. These files should then be useable with all document styles.
In such a multilingual document a user would specify the languages used as options to the \documentstyle command. He would also want a mechanism to be able to switch between these languages in a simple way. When he would use TEX version 3.0 for the processing of his document, he would also want the hyphenation to come out right for the different languages.