---
- name: Install locales
  apt:
    name: locales

- name: Create default locale
  locale_gen:
    name: "{{ locales__default }}"

- name: Configure locales
  debconf:
    name: locales
    question: locales/default_environment_locale
    value: "{{ locales__default }}"
    vtype: select
  notify: Rebuild locales database
...