Reasons:
* Searching translated QML error messages in Finnish with
  a search engine probably won't return many results,
  making troubleshooting harder.
* Localized error messages in stderr or error logs like
  .xsession-errors or systemd journal make reporting bugs harder.
* These messages are meant only for software developers and Finnish
  localization of Qt is targeted for localizing Qt-based applications,
  not developer tools.
* Practically all Finnish-speaking developers using Qt can be expected
  to know enough English when it comes to these error messages.
  End users won't understand them anyway.
* There doesn't exist much material about Qt in Finnish and
  the translations of some technical terms aren't that obvious
  or established.

Some error messages are still translated. Those are thought to be
useful for people other than developers and for those who might not
know enough English to understand the error message in English, but
who are able to solve the problem given the localized error message.

Change-Id: I3663825fb028b27edcb05b86620e53f7e3289f24
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>