Since Drupal 8 utilizes Twig templates, we cannot make a string translatable with the use of the t() function.
The solution to this problem is the Twig {% trans %} tag. This tag exposes the included string to the translation layer of Drupal 8.
Example:
{% trans %} This string will be avaiable for translation at the "User interface translation" of Drupal 8. {% endtrans %} Filters can also be used with the {% trans %} tag, even though some filters may not work properly. In that case, you may have to create a variable outside the {% trans %} tag.