Please use following Java code snippet in order to set language field in tag tab of object properties:
String inputFile = dataDir + "Language.pdf";
String outputFile = dataDir + "45696_out.pdf";
Document document = new Document(inputFile);
// Get TaggedContent
com.aspose.pdf.tagged.ITaggedContent taggedContent = document.getTaggedContent();
taggedContent.setTitle("Language setting example");
// Set Language for Document
taggedContent.setLanguage("es-ES");
com.aspose.pdf.tagged.logicalstructure.ElementList elementList = taggedContent.getRootElement().getChildElements();
com.aspose.pdf.tagged.logicalstructure.elements.bls.ParagraphElement p1 = (ParagraphElement)elementList.get_Item(0);
com.aspose.pdf.tagged.logicalstructure.elements.bls.ParagraphElement p2 = (ParagraphElement)elementList.get_Item(1);
// Set Language for Structure Element
p1.setLanguage("es-ES");
p2.setLanguage("en-US");
document.save(outputFile);
Please note that above code snippet can be used only with Aspose.PDF for Java 18.12 or higher.