According to a post in this forum, Aram Jabbari (the Atlus Public Relations manager) mentions the following:
There is no Japanese audio, only English. We really, truly try to
explore this option wherever possible. It just wasn’t something we
could do for Catherine.
In the same comments section, he also says
There is no Japanese voice option in the game. For the folks out there
who simply must have it, you’re right in that importing is the way to
go. It’d be a shame, though. We have a heck of a cast for the NA
release, and they do every bit of justice and then some to the
original audio track!
According to this forum (I do not know how legitimate this is), the developers also said the following:
While we certainly respect your preference and, as weve stated before,
always explore options to include a toggle with the original Japanese
voices, it should be noted that Catherines story and characters
inhabit a generic AMERICAN city. Hence everything in Stray Sheep,
their attire, etc. being in English.
And while we recognize the numerous comments from folks adamant that
its Japanese or nothing for them, we cant help but feel like those
gamers are going to miss out on what is, in our view, one of our best
localizations to date, and a fantastic English dub to boot.
Again, thanks for your thoughts. Were certainly always open to