If you have 1 language and you import language pack, that has 5 new languages, then it will fail with SQL error, that no l6_Translation column exists.
This happens, because there are only columns for first 5 languages after clean in-portal installation.
I think, that after new record is created in Languages database table we should also create corresponding new columns in all database tables, that have tnraslatable fields in them. Not sure if this happens already (maybe after language import was finished) or after each new language is created (as I would like it to work).
It seems, that problem was there right after we changed how phrases/e-mail events are stored in 5.1.0.