Recently, this query came up in the Seaside mailing list:
Looking for advice on best way to handle following situation: same application running with different database on different images on different machines where application code is the same but some key configurations are different such as various locale items like number formatting, currency symbol and large scale text changes do to different languages being used.
Rather than give you the stock market-speak from me, the product evangelist, I'll let a customer (Boris Popov) answer from the same thread:
The VisualWorks version of Seaside supports per-session locales and message catalogs dealing with both formatting and language issues AFAIK. I was going to look at that closer in a week or two and could report back if you're interested.
Although, that should be broadened to Cincom Smalltalk - you get that kind of thing in VW and ObjectStudio.