Thanks for the review. I just modified and committed it. Could you take a look?

Awesome! Another feature in development version. 👍

By the way, there is room for improvement about having to restart the application to apply the settings. Have you tried to make that work? We have the same problem when changing the language, but I suppose there could be problems due to Qt limitations (I haven't investigated it myself though). But maybe in this case it's just a matter of calling Settings::setValue() instead of invoking QSettings directly, and then get MainWindow to call reloadSettings(). Maybe a call to accept() at the end of PreferencesDialog::importSettings() would make the trick? I suppose that would do it, since it is what "restore defaults" is doing.

Yes, that's a good point.

It can be applied immediately by
call accept() in PreferencesDialog.cpp:importSettings(),
and call m_hCache.clear() in Settings.cpp:importSettings()

However, since the 'language' is also included in the settings file, I decided to request a restart.
If necessary, we can detect if there is a language change and only require a restart.

Yes, that makes sense.

Which method do you think is better?

1. Keep the old way
2. If the language settings is not changed, the settings is reflect immediately(work like 'Restore Defaults')
3. When the language settings is changed, a warning indicating to restart
4. When the language settings is changed, restart via code after warning(with QApplication, QProcess)

I think 2 and 3 is the best approach. 3 should reuse the current message dialog for notifying the user.

One more thing, I think we need save settings before export settings.
What do you reckon? @mgrojo

However, since this closes the PreferencesDialog and opens the FileDialog, it may be a little unnatural.
I have prepared a screencast to help you understand. https://youtu.be/ZM6wYA4II-g

I see. Having these buttons in the Preferences dialog complicates the implementation. Maybe you have to split (or add a parameter to) saveSettings so you can save the data without calling accept, and call accept once the file has been chosen and saved.

Cool, this is a simple fix so I just committed it to the master branch without pr. 0031d9a