Do NOT expect the culture on your thread to be communicated up to the Web API.

The ASP.NET Web API will not have this context. If you need it to speak you as you "think" you are speaking to it, I guess you'll either have to hand in an encoding for a culture or get back codes for messages which have to be combined with the current culture to do some fashion of message lookup. Some notes on this are:

• http://stackoverflow.com/questions/28608009/web-api-unable-to-set-culture
• http://stackoverflow.com/questions/20601578/async-webapi-thread-currentculture