ORA-12899 when inserting from sqlplus, but ok with jdbc
I have the same character set:

SELECT value FROM nls_database_parameters WHERE parameter = 'NLS_CHARACTERSET';


Result:

VALUE
-----------
AL32UTF8


I have NLS_LENGTH_SEMANTICS set to BYTE, but I can override this option in this way:

CREATE TABLE encoding (name VARCHAR2(5 CHAR));
INSERT INTO encoding VALUES('ééééé');

1 row created.


My NLS_LANG is: AMERICAN_AMERICA.UTF8, because my server is encoded UTF8.
But if I unset this environment variable:

unset NLS_LANG


and if i try again:

INSERT INTO encoding VALUES('ééééé');
ORA-12899; value too large for column "..."."..."."...." (actual: 10, maximum: 5)


so, yo can do a try and set your NLS_LANG variable, which is in the format

[NLS_LANGUAGE]_[NLS_TERRITORY].[NLS_CHARACTERSET]


And it would work. You can obtain this parameters from NLS_DATABASE_PARAMETERS.