Scala may be a way to get many of the benefits of Erlang and Haskell while also using a platform that is very successful and well-understood. And if I need to calculate what day of the week it is in 10 days in German, I know some library will exist for this. Scala could be snake oil, but it looks interesting.

I have to come to terms with my own ignorance. I'm not saying there isn't a good date library in Haskell. I'm saying I don't know if there is one, and as long as I'm learning a new language, I might as well choose something where I know at least some of those issues are definitely solved. This may cause some partisans to rage, but when choosing a language for a project, personal comfort is really the #1 issue.