Hey Ronny,
On Windows TurboActivate returns UTF16 strings, on Unix (Linux, Mac, Android, etc.) TurboActivate returns UTF8 strings.
In Xojo, the actual "string data" is stored in a "WString" object on Windows, and on other platforms the string data is stored in a "CString" object.
So, short answer: all strings are Unicode. The particular type of Unicode depends on the platform details (and historical quirks, like UTF8 not existing when Windows implemented Unicode strings, thus they're "stuck" with UTF16 as a Windows API default).