I am running an ASP.NET web site on IIS 7.5 with the culture and UI culture set to Invariant Culture in the settings. Client-based culture is set to false.
The IIS server is running on a German Windows Server 2008 R2, my machine is running English Windows 8.1 with Firefox set to accept en-us content first.
When the app generates an error message this message is in German. I can force it to be in English by changing the culture setting on IIS. Regardless of whether I turn Client-based culture on or off, it will always be in German.
In an answer to a similar question it was suggested that the invariant culture is based on English. Therefore I would assume error messages to be output in English.
How does IIS determine the language of the error message to output?