How to add custom Accept-Languages to Chrome for pseudolocalization testing?

Question

In Firefox

Use about:config

enter image description here

(There is a typo in qps-ploc in the screenshots, but you surely get the idea)

(Edit: refer to the comments for ways to avoid Chrome override the setting in new versions.)

Edit the file C:\Users\USERNAME\AppData\Local\Google\Chrome\User Data\Default\Preferences, and add:

{ ...

   "intl": {
      "accept_languages": "qps-ploc,en-us,en"
   },

   ...
}

For example:

enter image description here