in this tuto I'll show you how to get current language in page.html.twig.
First, in mytheme.theme add this:
/**
* @param $vars
*/
function mytheme_preprocess_page(&$vars) {
$language = \Drupal::languageManager()->getCurrentLanguage()->getId();
$vars['language'] = $language;
}
Then in my Twig file I use {{ language }} like this:
{% if language == 'en' %}
{{ "Do something" }}
{% else %}
{{ "Do something else" }}
{% endif %}
