Windev can also call functions from an external dll directly. Can I use that to call the TurboActivate.dll directly?
Yes. The integration classes for the languages (C#, VB.NET, Java, Delphi, etc.) are just thin wrappers that call the DLL directly. Plus the classes throw human-readable exceptions rather than using return codes on errors.
You can use any language you want without any external dependencies. You can use the TurboActivate.h file to see the return codes for the functions and what they mean.