Gettext works on the linux/unix ecosystem, but may make modding harder, as it doesn't allow us to modify the translation pool at runtime.

Integrating translations into the mod editor would also be difficult with gettext-based systems, and gettext's pipeline doesn't seem easily embeddable.

The date_time conversion doesn't really need the complexity of a full localisation system either, as the apoc date system is already simplified compared to real life, and we want to be matching that.

Part of removing boost #674