The @ft:lang attribute is used within the <ft:map> element to define the language of the FTML map.
The @ft:lang attribute is mandatory. If not provided, the FTML map is discarded.
The following lines show an example of the @ft:lang attribute:
<?xml version="1.0" encoding="UTF-8"?>
<ft:map ft:lang="en-US" ft:editorialType="book" ft:originId="48d2b" ft:title="Installation Guide">
...
</ft:map>