Oracle Import problem caused by different character sets

If that is the actual DDL you are using to create the table, you could use the NLS_LENGTH_SEMANTICS parameter. If you set that to CHAR rather than the default of BYTE, a VARCHAR2(5) will be allocated enough space to store 5 characters in the database character set (potentially up to 20 bytes) rather than 5 bytes (which could allow just 1 character).

Unfortunately, changing the NLS_LENGTH_SEMANTICS probably won't be terribly helpful if you're relying on the import process to create the table-- the dump file will inherently add the CHAR or BYTE keyword so it would actually issue the statement

CREATE TABLE BDATA.Artikel(
    Key                   VARCHAR2(3 BYTE)  NOT NULL,
    Name                  VARCHAR2(60 BYTE) NOT NULL,
    Abkuerzung            VARCHAR2(5 BYTE)  NOT NULL
);

You don't have a choice of character set on XE so you cannot change it to suit the database you are trying to import. Would it be practical to migrate the source database before export?

The import should work, but character set conversion might mean some text columns with non-ascii characters won't look the same after the import. And rows can be rejected if they are too long in the new character set.

In your case, you are converting to UTF8, which will mean it is possible for a single byte character to grow during conversion to 2 (or more in theory). You may need to increase the column size before export or adjust the target schema and import the data in a separate step. See here for other possible data truncation problems

The Easiest way: (Shutdown neccesary):

First, Connect as sysdba:

sqplus / as sysdba

Next, execute the following script:

alter system set nls_length_semantics=CHAR scope=both;
shutdown;
startup restrict;
alter database character set INTERNAL_USE WE8ISO8859P1;
shutdown;
startup;

It worked for me in a Oracle 12c Standard Two Edition

Taken from: http://www.blogdelpibe.com/2015/05/como-solucionar-el-error-ora-12899.html