The Irrlicht Engine is a high performance real-time 3D engine written and usable in C++, and also available for .NET languages. It is completely cross-platform, using D3D, OpenGL, and its own software renderer.
SecondLanguage lets you use Gettext files in .NET without a lot of hassle. It can read and write both .mo and .po, and fully supports message contexts and plural forms. A C-style printf formatter is included, so you don't have to use .NET-specific translations.