Use standard library style members of wxArrayString (and wxString) ...

... which will make it easier to change the types of those containers to
std::vectors of other string-like classes

for wxString,

IsEmpty => empty
Clear => clear
Alloc => reserve

for wxArrayString,

Count => size
GetCount => size
IsEmpty => empty
Add => push_back
Clear => clear
Empty => clear
Sort => std::sort (only with default comparator)
SetCount => resize
Last => back
Item => operator []
Alloc => reserve

src/Prefs.cpp

@@ -219,7 +219,7 @@ void InitPreferences()
    }
 
    // Use the system default language if one wasn't specified or if the user selected System.
-   if (langCode.IsEmpty())
+   if (langCode.empty())
    {
       langCode = GetSystemLanguageCode();
    }