---
- name: Install locales
  locale_gen:
    name: "{{ item }}"
    state: present
  loop: "{{ [locales_default] + locales_additional }}"

- name: Select default locale
  debconf:
    name: locales
    question: locales/default_environment_locale
    value: "{{ locales_default }}"
    vtype: select
  notify: Reconfigure locales
...