Trouble finding the right records

Hello, I’m creating a multilingual blog, where a translator would
translate single posts into several languages. I’m having some trouble
searching and comparing records.

My database is set up like this:
Posts: id, body, original_id, language_id
Languages: id, name

A single post, translated into several languages is grouped by the
number in ‘original_id’, like this:

http://www.harryvermeulen.nl/database.jpg

I’m looking for a way to find all the posts in (for example) english,
that do not have a translation in (for example) japanese yet.

I hope I’m making sense. I’m fairly new at web development, I hope I’m
in the right place to ask this question.

Kind regards,
Harry