You can create one fulltext index per table, that's true - but that index doesn't have to be for just a single language.
If you want, you can add some language hints to your CREATE FULLTEXT INDEX statement - if e.g. one column is the English text, while another one is the German description.
CREATE FULLTEXT INDEX ON ProductDocs
(DocSummary,
DocContentEnglisch TYPE COLUMN FileExtension LANGUAGE 1033,
DocContentGerman TYPE COLUMN FileExtension LANGUAGE 1031)
........
But you don't have to. SQL Server Fulltext indexing will work with multiple languages, no problem.
Check out Understanding Fulltext Indexing in SQL Server and SQL Server Full Text Search Language Features for more details.