demo.php

<?php
/**
 * writeToExcelFiles
 *
 * $messages is an array of this format:
 *  [
 *      'de' => [
 *          'categoryA' => 
 *              'text in line 1',
 *              'text in line 2',
 *          ],
 *          'categoryB' => 
 *              'text in line 1',
 *              'text in line 2',
 *          ],
 *      ],
 *      'en' => [ ... ],
 *  ]
 */
protected function writeToExcelFiles($messages, $excelDir)
{
    foreach ($messages as $language => $categories) {
        $excel = new PHPExcel();
        $index = 0;
        foreach ($categories as $category => $sources) {
            $sheet = new PHPExcel_Worksheet($excel, $category);
            $excel->addSheet($sheet, $index++);
            $sheet->getColumnDimension('A')->setWidth(60);
            $sheet->getColumnDimension('B')->setWidth(60);
            $sheet->setCellValue('A1', 'Source', PHPExcel_Cell_DataType::TYPE_STRING);
            $sheet->setCellValue('B1', 'Translation', PHPExcel_Cell_DataType::TYPE_STRING);
            $sheet->getStyle('A1:B1')->applyFromArray([
                'font' => [
                    'bold' => true,
                ]
            ]);
            $row = 2;
            foreach ($sources as $source) {
                $sheet->setCellValue('A'.$row, $source, PHPExcel_Cell_DataType::TYPE_STRING);
                $sheet->getRowDimension($row)->setRowHeight(-1);
                $row++;
            }
            $sheet->getStyle('A2:B'.$row)->getAlignment()->setWrapText(true);
        }
        $excel->removeSheetByIndex($index);
        $excel->setActiveSheetIndex(0);
        $writer = new PHPExcel_Writer_Excel5($excel);
        $writer->save($excelDir.DIRECTORY_SEPARATOR.$language.'.xls');
    }
}