I think we are talking about different things
I'm talking about a shortcode.
that will be replaced with JText::__('XXXXXXX') by the framework.
We have this in a custom plugin made by us and is very effective.
It saves us a lot of work when building multilangue sites.
Image if you want to make a article/module that is multilangue, you could use that shortcodes (with custom languague overrides if needed) and create only a multilangue article/module
instead of making 1 article/module for each languague you have in the site.
It's a feature suggestion not a bug fix