Represents the "Lang" entry of the catalog dictionary object.

It is an optional entry defined as part of the PDF 1.4 specification.

It contains a string representing a PDF string object.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 28, page 74.

Adobe Supplement to the ISO 32000, BaseVersion: 1.7, ExtensionLevel: 3; Table: 3.25, page 23.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 29, page 100.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 242, page 458.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 245, page 555.

The Lang entry specifies the natural language of the document's content as a Unicode language tag. This default language applies to all text in the document unless overridden at a lower level in the structure tree.