For packages containing multibyte characters we get that (ut_coverage_html_reporter)

ORA-06502: PL/SQL: numeric or value error: character string buffer too small
ORA-06512: at "UT3.UT_RUNNER", line 87
ORA-06512: at "UT3.UT_RUNNER", line 111
ORA-06512: at "UT3.UT", line 292
ORA-06512: at "UT3.UT", line 267
ORA-06512: at line 2

Oracle 11.2 docs:

Declaring Variables for Multibyte Characters
The maximum size of a CHAR or VARCHAR2 variable is 32,767 bytes, whether you specify the maximum size in characters or bytes.
When declaring a CHAR or VARCHAR2 variable, to ensure that it can always hold n characters in any multibyte character set, declare its length in characters—that is, CHAR(n CHAR) or VARCHAR2(n CHAR), where n does not exceed FLOOR(32767/4) = 8191.

Declaring with 32767
function clob_to_table(a_clob clob, a_max_amount integer := 32767, a_delimiter varchar2:= chr(10)) return ut_varchar2_list

Simple testcase

1. Single-byte "q"

declare
  c varchar2(32767 char);
begin
  c := rpad('q',32767,'q');
end;
/

OK
2. Multibyte "Ж" (Cyrillic)

declare
  c varchar2(32767 char);
begin
  c := rpad('Ж',32767,'Ж');
end;
/ 

Failed (numeric or value error: character string buffer too small)
3. Multibyte "Ж" (Cyrillic), rpad for 32k/2

declare
  c varchar2(32767 char);
begin
  c := rpad('Ж',32767/2-1,'Ж');
end;
/  

OK