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ZipArchive PHP function not support filenames that contains national characters. (Reason: UTF-8 filenames not supported in ZipArchive fuction at this time, only DOS charshets supported).
replace (in filebrowser.module) $zip->addFile($file_data['path'], $file_name); by $zip->addFile($file_data['path'], iconv("UTF-8","CP852",$file_name));
Change the CP852 codepage for your own code page (CP437, CP850 etc.).