To prepare for translation support, this makes all of the widgets
cognizant of the language change event that occurs whenever
installTranslator() is called and automatically retranslates their text
where necessary.
This is important as calling the backing UI's retranslateUi() is often
not enough, particularly in cases where we add our own strings that
aren't controlled by it. In that case we need to manually refresh the
strings ourselves.
These slots are only ever attached to event handling mechanisms within
the class itself, they're never used externally. Because of this, we can
make the functions private.
This also removes redundant usages of the private access specifier.
Keeps the individual behaviors in their own functions, and cleanly
separate. We can also do a little better by converting the relevant IDs
within the core to a QString only once, instead of converting every
string into a std::string.
Disambiguates what the string represents to help translators more easily
understand what it is that they're translating. While we're at it, we
can move the code to its own function, so that we don't need to specify
the same string twice.
