Multilingual Search using lucene

I am doing a multilingual search. And I will use lucene as the tool to do it.

I have the translated contents already, there will be 3 or 4 languages of each document.

For indexing and search, there could be the 4 strategies, For each document/contents:

1. each language are indexed in different index/directory.
2. each language are indexed in different document but in the same index.
3. each language are indexed in different Field but in the same document.
4. all the languages are indexed in the same Field in a document

But I have not test each of the way yet, could anyone experienced tell me which one is a better way to do the multilingual search?

Thanks!