For me, clicking swap does not reverse the Auto-detect and English positions so I have to go throught a manual process every single time
When I open Bing Translator using an "English" PC in Spain the two Language drop-down options (from and To) are frustrating.
If I am on an English PC in Spain the default offering of translating to English is resonable but insuffiecient and incomplete.
The most likely user case scenario is the I want to translate either from Spanish to English or English to Spanish.
It so happens in my case I mostly want to translate from Spanish to English, however to achive this I have use the list box language selections options and then swap / reverse everytime. Surely the from - to language options should default to English and Spanish, so that I just click the swap button to reverse the "direction" of the translation I require rather than having to go throught this manual process every time.
Presumably you are using some combination of culture detection and geo location and the logic of the current implementation may give be give me the same type of user expereince if I move to another coutry.
keep up the good work.