Spreadsheet::WriteExcel requires Unicode characters to be in Perl's UTF8 format. So you will need to convert them from the encoding that you are reading them in to UTF8 (perhaps using Encode) before writing them back to a WriteExcel file.

I don't have an example for cp1250 but here is an example with cp1251.

See also the Unicode section of the Spreadsheet::WriteExcel docs.

--
John.