Generates loacles defined in `gen_locales`, sets `LANG`, `LC_MESSAGES`, and `LANGUAGE` to the values of
`lang`, `lc_messages` and `language` respectively. These have the following defaults:

```
gen_locales:
  - en_US.UTF-8
  - en_GB.UTF-8

lang: en_US.UTF-8
lc_messages: "{{ lang }}"
language: "en_US:en"
```