Read non-Unicode, non-English text from SQLite database
All the normal functions in the SQLite C API use UTF-8. The C# SQLite driver automatically converts between UTF-8 and the C# string encoding.
If you do not get correct data from your C# program, then it's likely that the C++ application did not actually UTF-8. This is confirmed by the fact that the C++ application gives different results with different code pages.
If possible, fix the C++ application, or convert the data in the database from the original encoding to UTF-8. As a last resort, you could change your C# application to read all the strings as blobs and then convert them from the original encoding to UTF-8. (In any case, you need to know what the original encoding is.)