How specify a list value as variable in ansible inventory file?

With complex variables, it's best to define them in a host_vars file rather than in the inventory file, since host_vars files support YAML syntax.

Try creating a host_vars/127.0.0.1 file with the following content:

---
timezone: Europe/Amsterdam
locales:
  - en_US
  - nl_NL

You can pass a list or object like this:

[example]
127.0.0.1 timezone="Europe/Amsterdam" locales='["en_US", "nl_NL"]'