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

You can pass a list or object like this:

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

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

Ryler's answer is good in this specific case but I ran into problems using other variations with the template module.

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

Is his original example and works fine.

The following variations work with template. Basically if it's a string you must remember to use the internal double quotes or the entire structure is parsed as a single string. If it's only numbers or "True" or "False" (not "yes") then you're fine. In this variation I couldn't make it work with template if it had external quotes.

I haven't done an exhaustive check of which internal use cases they do and do not break other than the template module.

I am using Ansible 2.2.1.

[example:vars]
# these work
myvar1=["foo", "bar"]
myvar2=[1,2]
myvar3=[True,False]

# These fail, they get interpreted as a single string.
myvar4=[yes, no]
myvar5=[foo,bar]
myvar6='["foo", "bar"]'

you can try split

#inventory file
[example]
127.0.0.1 timezone="Europe/Amsterdam" locales="en_US","nl_NL"

#role file
---
- debug: msg="{{ item }}"
  with_items: locales.split(',')