Support package.json i18n key and show a hint in case the extension is t...

...ranslated into the users language

Implements #6835.
Ahh, yeah, I see that does get a bit tangled. It seems a shame to create a new "i18nUtils.js" for this one function, but I can imagine us having more functions over time and I don't like the idea of duplicating this function, small though it is.

What do you think about just having a new file?