character(n)

select * from "t"@PG_LINK

SQL> desc "t"@PG_LINK
 Lь                                        ¦єёЄю?   Tшя
 ----------------------------------------- -------- ----------------------------

 f                                                  NVARCHAR2(500)
 f2                                                 NVARCHAR2(2000)


Поля character бОльшего размера Oracle "не видит".

select *
from nls_database_parameters
where parameter like 'NLS_CHARACTERSET'
/
 
NLS_CHARACTERSET - CL8MSWIN1251

show server_encoding;

"WIN1251"

HS_LANGUAGE=RUSSIAN_RUSSIA.CL8MSWIN1251