There are some blank lines at the bottom of spanish.php language which cause HEADERS ALREADY SENT error.
Some strings must be added to this archive also
DEFINE('_COM_SEF_NOACCESS','Unable to access');
DEFINE('_COM_SEF_FATAL_ERROR_HEADERS','FATAL ERROR: HEADER ALREADY SENT');
DEFINE('_COM_SEF_UPLOAD_OK','File was successfully uploaded');
DEFINE('_COM_SEF_ERROR_IMPORT','Error while importing:');
DEFINE('_COM_SEF_INVALID_SQL','INVALID DATA IN SQL FILE :');
DEFINE('_COM_SEF_NO_UNLINK','Unable to remove uploaded file from media directory');
DEFINE('_COM_SEF_IMPORT_OK','Custom URLS were successfully imported!');
DEFINE('_COM_SEF_WRITE_FAILED','Unable to write uploaded file to media directory');
DEFINE('_COM_SEF_EXPORT_FAILED','EXPORT FAILED!!!');
DEFINE('_COM_SEF_IMPORT_EXPORT','Import/Export Custom URLS');
DEFINE('_COM_SEF_SELECT_FILE','Please select a file first');
DEFINE('_COM_SEF_IMPORT','Import Custom URLS');
DEFINE('_COM_SEF_EXPORT','Backup Custom URLS');
//Added by Leon
define('_FULL_TITLE', 'Full Title');
define('_TITLE_ALIAS', 'Title Alias');
define('_COM_SEF_SHOW_CAT', 'Mostrar categorÃa');
Thanks