sonata-project/exporter/lib/Exporter/Writer/CsvWriter.php

    /**
     * {@inheritdoc}
     */
    public function write(array $data)
    {
        if ($this->position == 0 && $this->showHeaders) {
            $this->addHeaders($data);

            ++$this->position;
        }

        mb_convert_variables('SJIS-win', 'UTF-8', $data); // 追加

        $result = @fputcsv($this->file, $data, $this->delimiter, $this->enclosure);

        if (!$result) {
            throw new InvalidDataFormatException();
        }

        ++$this->position;
    }