Hello.
To see this issue add to test LanguageTagTests.ExtractLangTagFromUrl following lines:

ExtractLangTagFromUrlHelper("/Api/City", "Api", "/City"); // Pass!
ExtractLangTagFromUrlHelper("/Api/City", "", "/Api/City"); // I expected. It failed.

So it extracted "Api" as langtag and url become "/City".
I expect from this function to only extract tag for language that is in currently supported languages list LanguageHelpers.GetAppLanguages(). What do you think about it?

Thanks for your great work.