Which language / framework if any?

[updated]

Your going to need some kind of framework - even if it's as simple as JQuery - http://i18next.com/docs/ecosystem/

Then - follow the sample here: http://i18next.com/translate/context/

{
  "debug": true,
  "lng": "en",
  "fallbackLng": "en",
  "backend": {
    "loadPath": "locales/{{lng}}/{{ns}}.json"
  }
}

So put your translation files in the loadPath structure - then theres no duplication of content. Using a framework, you'll replace the text in the selectors and the i18next code will take care of replacing the strings.

If you're working with seperate files, you can just make one folder 'translations' or 'i18n' and put the files there? Keep it simple ;)

Or are there restrictions which apply to your situation?

In my own case, the translations are stored in a database, so that's easy to manage.