For https://www.reddit.com/r/haskell/comments/3l3f1s/ann_googletranslate_written_w_servantclient/

langs.hs

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE StandaloneDeriving #-}

module Langs where

import Data.Proxy
import GHC.TypeLits

data Language (code :: Symbol) where
    English :: Language "en"
    Dutch :: Language "nl"
    French :: Language "fr"

deriving instance Show (Language code)

doSomething :: forall code. KnownSymbol code => Language code -> String
doSomething lang = "The code for " ++ show lang ++ " is " ++ show code
  where
    code = symbolVal (Proxy :: Proxy code)

main :: IO ()
main = do
    putStrLn $ doSomething Dutch
    putStrLn $ doSomething English

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