Not sure why you think Articles Anywhere would be able to do something like that.
A language string has nothing to do with an article.

You could use Sourcerer to echo out a language string via PHP using the Joomla Text class.

Either use Sourcerer or ReReplacer Pro to place stuff like:
You could use ReReplacer Pro to make a custom shortcode for it. So you could do something like: {text MY_LANGUAGE_STRING}, or [[MY_LANGUAGE_STRING]], or whatever other shortcode syntax you want.
docs4.regularlabs.com/rereplacer/example...ic-plugin-style-tags

What do you mean with files?

Cache files… well that is all down to how you set up caching.
An article in 8 different languages will create and need 8 cache files. That's how caching works.

I am not sure how things will function in YoothemePro.
You can try out the free version of ReReplacer to see if simple replacements will work.
If so, then replacing with php (using the Pro version) should also work.

Then the Pro version won't be able to replace things either.