Statically linked Haskell program in Docker
You encountered a feature of GHC runtime system. Even the application is static, it needs some auxiliary files, locale files are one of them.
See https://ghc.haskell.org/trac/ghc/ticket/7695 and https://ghc.haskell.org/trac/ghc/ticket/10298
As you can see, that will be fixed in 7.10.2 (which at the moment is right behind the corner).
https://github.com/snoyberg/haskell-scratch image lists hopefully all files you need in the minimal container.