Let's hope that the std::exception::what() returns either a 7-bit

string or an UTF-8 string. Let's convert it to wxString before
showing an error message box.
boost::system shall return UTF-8 localized error messages as long
as we set -DBOOST_SYSTEM_USE_UTF8 in the top most CMakeFiles.txt,
which we do.

src/slic3r/GUI/GUI_App.cpp

@@ -608,7 +608,7 @@ static void generic_exception_handle()
         std::terminate();
         throw;
     } catch (const std::exception& ex) {
-        wxLogError("Internal error: %s", ex.what());
+        wxLogError("Internal error: %s", wxString::FromUTF8(ex.what()));
         BOOST_LOG_TRIVIAL(error) << boost::format("Uncaught exception: %1%") % ex.what();
         throw;
     }