The SYS_COLLATIONS system table holds the data for all the defined collations. It has the following structure:

CREATE TABLE SYS_COLLATIONS (
    COLL_NAME VARCHAR,
    COLL_TABLE LONG VARBINARY,
    COLL_IS_WIDE INTEGER);

COLL_NAME is the fully qualified name of the collation (it's identifier)

COLL_TABLE holds the collation table (256 bytes or 65536 wide chars)

COLL_IS_WIDE show the collation's type (0 for CHAR and 1 for NCHAR). Note that a 8bit collation cannot be used by a NCHAR data and vice versa.

Collation can be deleted by deleting its row from SYS_COLLATIONS.

[Note] Note

The collation will still be available until the server is restarted, as it's definition is cached into memory.