Drupal 8 incorporates a new templating system for HTML output generation called Twig – see the Drupal 8 theme guide. Twig does not use a native PHP format, so it needs its own solutions for string translations.
Simple text translation is possible with the 't' (or 'trans') filter, while a whole {% trans %} block is supported (as defined by the Twig i18n extension) for more complex scenarios, such as strings with placeholders and singular/plural combinations.
These two do the same; they run the text through t():
Example 1 with t or trans filter:
{{ 'Hello Earth.'|trans }}
{{ 'Hello Earth.'|t }}
Example 2 with {% trans %}:
{% trans %}
Submitted by {{ author.username }} on {{ node.created }}
{% endtrans %}
Example 3 translation with variables:
<p class="submitted">{{ "Submitted by !author on @date"|t({ '!author': author, '@date': date }) }}</p>
Plural Translations
Making plural translations are now also even easier, just implement a {% plural ... %} switch!
Example:
{% set count = comments|length %}
{% trans %}
{{ count }} comment was deleted successfully.
{% plural count %}
{{ count }} comments were deleted successfully.
{% endtrans %}
Values are escaped by default. The 'raw' filter can be used to skip escaping. The 'placeholder' filter can be used to form a placeholder. The default behavior is equivalent to @ in t(), while 'raw' matches ! and 'placeholder' matches %:
{% set string = '&"<>' %}
{% trans %}
Escaped: {{ string }}
{% endtrans %}
{% trans %}
Raw: {{ string|raw }}
{% endtrans %}
{% trans %}
Placeholder: {{ string|placeholder }}
{% endtrans %}
These will translate Escaped: @string, Raw: !string and Placeholder: %string respectively.
{% trans %} & Twig Filters
Filtering Twig variables inside the {% trans %} tag will generally work. However, some of these filters may not work properly or at all. If you are not seeing the desired result or you are receiving fatal errors/WSOD you may need scale down what you are trying to do inside the {% trans %} tag. Create a new Twig variable outside of the tag with this filter applied:
{% set date = node.created|format_date('medium') %}
{% trans %}
Node was created on {{ date }}.
{% endtrans %}
Context and Language Options
The t() and format_plural() functions have an $options parameter that can provide additional context or allow a specific language to be chosen for translation. To pass these options in the {% trans %} tag, use the with { ... } syntax in the opening tag:
{% trans with {'context': 'Long month name', 'langcode': 'hu'} %}
May
{% endtrans %}
{% trans 'May' with {'context': 'Long month name', 'langcode': 'hu'} %}
This will translate May as a long month name into Hungarian specifically.
