OpenCC bindings.
Open Chinese Convert (OpenCC, 開放中文轉換) is an opensource project for conversions between Traditional Chinese, Simplified Chinese and Japanese Kanji (Shinjitai). It supports character-level and phrase-level conversion, character variant conversion and regional idioms among Mainland China, Taiwan and Hong Kong. This library is the Haskell bindings.
opencc-hs
This library contains both high-level and low-level bindings to OpenCC, Open Chinese Convert. This library is an experiment on Haskell FFI and is not intended for industrial use (at least for now). But since this library is extremely simple, you are welcome to review the code and decide for yourself.
Comparison
hopencc is an existing Haskell library that does the same thing, but that library only provides the IO-flavor binding here. hopencc copies the data, while opencc-hs doesn't (taking advantage of the internal representation of bytestrings).