Shopify `t` filter doesn't allow `default:` filter

I'm not sure where to post this so I'm posting it here.

I'd like to allow for default language to be used or default filter fallback.

Is there any way to achieve this?

I'm trying to build the translation system around product tags. Some of these could be brand names so there's no need to translate those and default fallback would make perfect sense, but I cannot achieve this easily. I need to hack something along these lines:

Instead of:

{{ tag | t | default: tag }}

I have to do something along the lines of:

{% assign translated_tag = tag | t %}
{% if translated_tag contains 'translation missing' %}
  {% assign translated_tag = tag %}
{% endif %}

Start by locating the implementation of the Liquid t filter and how filter chaining handles default:; the issue provides the two template examples to compare. Check whether missing translations can participate in the fallback and add coverage for the requested behavior, with the chained expression producing the original tag when translation is unavailable.