Exception &1 for creating language &2 for index category &3 Rcode: &4

What causes this issue?

An error occurred when generating a language for an index category.
Documents belonging to this language and index category cannot be
indexed.

System Response

Exceptions:
1:
Unknown index category ID (CATID_UNKNOWN)
2:
Index category is deactivated (IDXCAT_IS_INACTIVE)
3:
Language index already created (LANGU_ALREADY_DEF)
4:
Invalid language code (LANGU_NOT_VALID)
5:
RFC_SYS_FAILURE
6:
RFC_COM_FAILURE
7:
NO_RFC_DEST
8:
XERROR
9:
Others

How to fix this error?

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.