I'm not so sure that checking just the left side will be correct for composite keys.
This query works under pgAdmin, but I haven't tested through Hibernate. I don't even know if I can give such parameters if they're not a composite primary key class. I'll get back to you on that, hopefully within 2 weeks. I have other things to do and it doesn't seem like a big priority.

SELECT * from documents d WHERE (d.target_id, d.lang_id) IN ((3185,'de'), (3185,'en'))