Fix pluralization for og:description

Added a new "pluralize" macro to make this easier, so I'll go back and
implement this in the other places as well.

tildes/tildes/templates/macros/utils.jinja2

@@ -0,0 +1,15 @@
+{# Copyright (c) 2019 Tildes contributors <code@tildes.net> #}
+{# SPDX-License-Identifier: AGPL-3.0-or-later #}
+
+{% macro pluralize(counter, base_word, plural_word=None) %}
+  {% if not plural_word %}
+    {% set plural_word = base_word~"s" %}
+  {% endif %}
+
+  {%- trans counter=counter -%}
+    {{ counter }} {{ base_word }}
+  {%- pluralize -%}
+    {{ counter }} {{ plural_word }}
+  {%- endtrans %}
+{% endmacro %}
+

tildes/tildes/templates/topic.jinja2

@@ -9,12 +9,13 @@
 {% from 'macros/forms.jinja2' import markdown_textarea %}
 {% from 'macros/links.jinja2' import group_linked, username_linked %}
 {% from 'macros/topics.jinja2' import topic_voting with context %}
+{% from 'macros/utils.jinja2' import pluralize %}
 
 {% block title %}{{ topic.title }} - ~{{ topic.group.path }}{% endblock %}
 
 {% block meta_og_tags %}
   <meta property="og:title" content="{{ self.title() }}">
-  <meta property="og:description" content="{{ topic.num_comments }} comments in the discussion of this {{ "link" if topic.is_link_type else "post" }} on Tildes">
+  <meta property="og:description" content="{{ pluralize(topic.num_comments, "comment") }} in the discussion of this {{ "link" if topic.is_link_type else "post" }} on Tildes">
 {% endblock %}
 
 {% block templates %}