Вы можете изменить свойства вашего JFileChooser как FileChooser.openButtonText
UIManager.put("FileChooser.acceptAllFileFilterText", "Directorios");
UIManager.put("FileChooser.lookInLabelText", "Localização");
UIManager.put("FileChooser.cancelButtonText", "Cancelar");
UIManager.put("FileChooser.cancelButtonToolTipText", "Cancelar");
UIManager.put("FileChooser.openButtonText", "Adicionar");
UIManager.put("FileChooser.openButtonToolTipText", "Adicionar ficheiro(s)");
UIManager.put("FileChooser.filesOfTypeLabelText", "Tipo");
UIManager.put("FileChooser.fileNameLabelText", "Ficheiro(s)");
UIManager.put("FileChooser.listViewButtonToolTipText", "Lista");
UIManager.put("FileChooser.listViewButtonAccessibleName", "Lista");
UIManager.put("FileChooser.detailsViewButtonToolTipText", "Detalhes");
UIManager.put("FileChooser.detailsViewButtonAccessibleName", "Detalhes");
UIManager.put("FileChooser.upFolderToolTipText", "Um nível acima");
UIManager.put("FileChooser.upFolderAccessibleName", "Um nível acima");
UIManager.put("FileChooser.homeFolderToolTipText", "Ambiente de Trabalho");
UIManager.put("FileChooser.homeFolderAccessibleName", "Ambiente de Trabalho"); UIManager.put("FileChooser.fileNameHeaderText", "Nome");
UIManager.put("FileChooser.fileSizeHeaderText", "Tamanho");
UIManager.put("FileChooser.fileTypeHeaderText", "Tipo");
UIManager.put("FileChooser.fileDateHeaderText", "Data");
UIManager.put("FileChooser.fileAttrHeaderText", "Atributos");
UIManager.put("FileChooser.openDialogTitleText","Adicionar Fotos");
UIManager.put("FileChooser.readOnly", Boolean.TRUE);
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