I think UniData is a bit of a red-headed stepchild in the Pick world. Certainly the reports I've seen seem to say that under the hood it doesn't do it like the other db's in the family.
Yes, I suspect internationalisation may be a bit of a pain, but it has been done. I haven't used it, but I haven't used internationalisation on linux either (I guess it's there, but I'm not conscious of it).
Limited depth hierarchies? In reality, how often do you blow off the end of Pick's ability? The tools aren't necessarily that good, but it handles between five and seven levels "out of the box". How many entities have attributes nested that deep?
You're right about Ardent acquiring the Uni products, but in reality, Ardent took over Informix. Yes, I know Informix the company bought out Ardent, but six months later the Informix board was gone, replaced entirely by Ardent people. The rumour is that IBM bought Informix for the Informix database, only to discover that the company's primary product by then was U2.
And as you say about Postgres, I don't know anything about it but I understood it could handle multivalue columns sort of thing. If you're going to be strictly relational, however, that's not allowed :-) Postgres is moving away from a pure relational db to a more NFNF model. Pick was there first ... :-)