Agreed, yargs (the CLI app that this was built for) has very basic requirements -- there are only a few dozen strings in the entire codebase.

Having said this I did make an effort to learn from prior work in the area, basing the library on: https://github.com/mashpie/i18n-node

A friend of mine who did a thorough literature review at PayPal also advocated formatjs.io -- although I think this is a little bit too much power for little old yargs.