[Interest] Support of russian language in QJson-classes

[Dmitrii Volosnykh]

Oliver, first of all, thanks for your input!

Source file is stored in UTF8, indeed. This was the first thing I
checked when encountered problems mentioned in my first letter.

What you advise is not applicable for my case, because the keys are
obtained from user input. It means that I can not hardcode them. That
was just minimal example reproducing the issue I faced.

As for setting the charset for the generated text file. Docs for
QJsonDocument::toJson() say:
"Converts the QJsonDocument to a UTF-8 encoded JSON document in the
provided format."
So, it seems, I am not supposed to bother.

Regards,
Dmitrii.