I changed the current culture to German and tested a title.

Thread.CurrentThread.CurrentUICulture = new CultureInfo("de");
Console.WriteLine(StringHumanizeExtensions.Humanize("Per anhalter durch die Galaxis", LetterCasing.Title));

The result seems to be Per Anhalter Durch Die Galaxis, but the expected result should be Per Anhalter durch die Galaxis.

Can you tell me if your title casing works in the same way as .NET's ToTitleCase (i.e. always caps the first letter of each determiner, preposition, etc.)?