Ny doc listing standard <=> Oracle character sets correspondencies

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
);

I am a little doubtful that this is exactly what you are looking for, but

host echo %nls_lang%;

ENGLISH_UNITED KINGDOM.WE8ISO8859P1

shows the client nls_lang environment variable on the client.

I don't think there will be a SQL query you can run to give the 'current' setting because AFAIK the server is not aware of what translation is done client-side, so any command to show the current setting will have to be native to the client - I used SQL Developer for the above command, but I assume it will work the same in SQL*Plus

--edit

from AskTom:

only the client knows their character set as well -- it is not available "in the database"

and

the character set describes what is stored in database.

the client makes their desired translated to character know [sic] to the database via the NLS_LANG settting.

If you were on 11.1+, you might have some joy with v$session_connect_info, because:

This information is pushed by OCI to the server ats login time.

But I discovered it would still depend on how you are connecting, eg from the JDBC Thin Driver you aren't using OCI and so the information isn't pushed