add translation strings

- add logic when default shelves used
- add trans strings in a few spots they were missing

bookwyrm/templates/snippets/shelf_selector.html

@@ -13,7 +13,14 @@
         <input type="hidden" name="book" value="{{ book.id }}">
         <input type="hidden" name="change-shelf-from" value="{{ current.identifier }}">
         <input type="hidden" name="shelf" value="{{ shelf.identifier }}">
-        <button class="button is-fullwidth is-small shelf-option is-radiusless is-white" type="submit" {% if shelf.identifier == current.identifier %}disabled{% endif %}><span>{{ shelf.name }}</span></button>
+        <button class="button is-fullwidth is-small shelf-option is-radiusless is-white" type="submit" {% if shelf.identifier == current.identifier %}disabled{% endif %}>
+            <span>
+                {% if shelf.identifier == 'to-read' %}{% trans "To Read" %}
+                {% elif shelf.identifier == 'reading' %}{% trans "Currently Reading" %}
+                {% elif shelf.identifier == 'read' %}{% trans "Read" %}
+                {% else %}{{ shelf.name }}{% endif %}
+            </span>
+        </button>
     </form>
 </li>
 {% endfor %}