Chrome.i18n

You can use the chrome.i18n infrastructure to implement internationalization across your whole chrome app or chrome extension.
To localize a chrome extension chrome.i18n is using a custom JSON format that you can either import and export manually on the dashboard or you can automate your Chrome extension translation process with the Applanga Localization CLI.

Website: https://developer.chrome.com/extensions/i18n

File Extension
.json
CLI format key
chrome_i18n_json
CLI Supported
true
SDK Supported
false
String Description Supported
true
Pluralization Supported
false

Example:

{
  "empty_string_key": {
    "message": ""
  },
  "with_description_key": {
    "message": "This key has a description in some file-formats.",
    "description": "Here is the description of the key"
  },
  "with_line_break_key": {
    "message": "This key has a line break\nin it."
  },
  "nested_key.level_one_a.level_two": {
    "message": "A deeply nested key."
  },
  "nested_key.level_one_b": {
    "message": "A nested key."
  },
  "plural_key[one]": {
    "message": "Plural key one"
  },
  "plural_key[other]": {
    "message": "Plural key other"
  },
  "plural_key[zero]": {
    "message": "Plural key zero"
  },
  "array_key[0]": {
    "message": "first entry"
  },
  "array_key[1]": {
    "message": "second entry"
  },
  "array_key[2]": {
    "message": "third entry"
  },
  "simple_key": {
    "message": "Most basic translation."
  }
}