How to get current language of node in twig?
A more elegant Drupal way without typing code:


Go to the Manage display of the content type of your node (/admin/structure/types/manage/YOUR_CONTENT_TYPE/display/full). Select your display mode (or use the default). You will notice the field 'Language', move it to the upper side so it gets out of 'Disabled'.
Once you have done that, the language of the node is available in Twig. You can access the id this way {{ node.langcode.langcode }}; or you can access the whole Object to get other data like the name {{ drupal_dump(node.langcode) }}