Error exp oracle XE on centos i have a problem when i try to export ...

Connected to: Oracle Database 11g Express Edition Release 11.2.0.2.0 - 64bit Production
Export done in WE8MSWIN1252 character set and AL16UTF16 NCHAR character set

About to export specified users ...
. exporting pre-schema procedural objects and actions
. exporting foreign function library names for user SEMESU 
. exporting PUBLIC type synonyms
. exporting private type synonyms
. exporting object type definitions for user SEMESU 
About to export SEMESU's objects ...
. exporting database links
. exporting sequence numbers
. exporting cluster definitions
EXP-00056: ORACLE error 12704 encountered
ORA-12704: character set mismatch
EXP-00000: Export terminated unsuccessfully

anyone? (i'll apreciatte)
You will have to export NLS_LANG env variable like mentioned here
http://docs.oracle.com/cd/E11882_01/server.112/e16604/ch_eleven.htm#sthref1049
If you use expdp, you don't need to do this...