I had a similar problem here, and since I got no answer to my post
and after seeing the recently posted "Synchronize Wordpacks for IPB 3.0 RC1 (v 1.0.0)" Hook, I decided to modify it, so that I can reuse my old IPB2.3.6 board translations.
During the process, I saw that "Synchronize Wordpacks" required a lot of queries, so I decided to change it a bit,
by using php arrays instead: probably this makes it a bit faster.
I could not avoid multiple insert or update queries though: I really don't know how to do batch (array) insert/update queries in IPB style(if this is possible somehow).
Instructions are provided as comments in the start of the file of the hook.
The Hook did a very nice work for me and updated my previous IPB2.3.6 translation!
Send your comments/questions here (or to the other thread) or and if some of you
find it useful, I can upload it to the Downloads section. hookUpdateTranslations.xml