Ekaitz Zárraga (i18n_yaml) responded via twitter:

I wanted to make it for learning and to cover my very specific problem in my other package called `schiumato` which is a simple static website generator.
I don’t like the JSON approach for the catalogs because JSON doesn’t handle correctly the newlines and the long strings.

That’s all.

I have to rewrite it and stuff but it works for the moment and solves my very specific task.
Hope this clarifies something.