Ok, thanks, I'll wait for the DBA's to perform the upgrade... a couple of years.
in the meanwhile i'll try storing the characters as Unicode.

Are you saying that parsing special characters will work with json functions in an oracle 18+ database regardless of the characterset. If I upgrade my 1252 database to oracle 18, then the json functions will work?

In 19c with a database character set of AL32UTF8, Json_object_t.Parse works with the first 1900 unicode characters. This includes any characters that require escaping.

DECLARE
    L_datos    CLOB;
    L_json    Json_object_t;
BEGIN
    select json_object('value' is listagg(unistr('\'||to_char(level-1,'fm000X'))) returning clob)
    into l_datos
    from dual
    connect by level <= 1900;
    L_json := Json_object_t.Parse (L_datos);
END;
/

Best regards,
Stew Ashton

I tested an indeed the issue is fixed in 19

SQL*Plus: Release 19.0.0.0.0 Version 19.5.0.0.0

SQL> SELECT value$ FROM sys.props$ WHERE name = 'NLS_CHARACTERSET' ;

VALUE$
--------------------------------------------------------------------------------
WE8MSWIN1252

SQL> declare
2
3 l_json_obj JSON_OBJECT_T;

4 5 begin
6
l_json_obj := JSON_OBJECT_T.parse(' { "MedicalConditionDiagnosis": "Sclérose latérale amyotrophique (maladie de Lou-Gehrig)" } ');

7 8 9 DBMS_OUTPUT.put_line('l_json_obj ' || l_json_obj.TO_STRING);
10
end; 11
12 /

PL/SQL procedure successfully completed.

convert function...until you upgrade.
That is what we are doing.

declare
l_json_obj JSON_OBJECT_T;
begin
l_json_obj := JSON_OBJECT_T.parse(convert('{ "MedicalConditionDiagnosis": "Sclérose latérale amyotrophique (maladie de Lou-Gehrig)" } ','AL32UTF8','WE8MSWIN1252'));
DBMS_OUTPUT.put_line('l_json_obj ' || l_json_obj.TO_STRING);
DBMS_OUTPUT.put_line('l_json_obj ' || l_json_obj.get_string('MedicalConditionDiagnosis'));

end;