Found a useful link:Free/open-source machine translation software
I think you can try some Rule-Based Translator like Apertium, Anusaaraka, OpenLogos or Maxin. But I think statistical machine translation systems can provide better translation quality if get adequate training. Moses has the widest community support and has been tried out by many localization companies and researchers. You can take a look at its translation quality here based on different training data and languages.
Other Option（You have to rely on network, they are not open sourced):
Microsoft Translator APIs
Microsoft Translator APIs provides Ajax, SOAP, HTTP accesses, it requires registration. But it is free. I think the Bing Translation API relies on it.
Mygengo Translation API
Gengo requires you to create an account first.
WebServiceX Translate API
A free webservice. Check its wsdl
Yandex API
