The presence of a character set in DBC.CharSetsV or DBC.CharTranslationsV does not mean it is active. The InstallFlag column in DBC.CharSetsV or DBC.CharTranslationsV is a good indication, but can be misleading if the table has been changed without performing a restart of the database.
ASCII, EBCDIC, UTF16, and UTF8 character sets, which are predefined and permanently loaded into the system, are always available. The character sets are not listed in DBC.CharTranslationsV.