Use system locale by default for i18n

[forivall]

Related: tableflip/nodebot-workshop#20

Ideally, use https://github.com/sindresorhus/os-locale to determine the default language, and if it's available for the workshopper, use it!

[martinheidegger]

@forivall I wanted to implement this a while back but never found the time to go for it. I would welcome a PR that adds this feature. Thank you for bringing this up!