it looks like that there is a problem with support of national characters in imported data file when method "Insert script" is chosen.
Table -> Import Data -> Open datafile "csv".
As far as in the preview window I'm seeing properly displayed national characters from csv data file and when I'm choosing "Insert" or "SQL Loader" method - data is properly imported to the table.
But when I'm using "Insert script" method, in generated script national characters are changed into "bushes":
SQL Developer: Version 3.2.20.09
OS: Windows XP SP3
Client code page: WIN-1250
Tested databases: 10g, 11g