To create functions in the C language, superuser access is required. Additionally, it is strongly advised against updating catalog tables directly. As you do not have superuser access, you were prevented from potentially causing significant issues.
If you do not possess superuser privileges (which is preferable, considering your recent attempts), you'll need to request your DBA to execute these statements on your behalf.
https://stackoverflow.com/questions/7014437/error-permission-denied-for-language-c