Problem is, each language version really should be considered a different lanaguage.
Maintaining any long (>10 year) lifed C++ is a massive PITA.
Ibe seen programmers start off MFC C++ style - C++90 + the stupid MS addons.
Then some has read the Design Pattern book, so you get 'patterns' in the code base from 95is-00ish.
Then they discover the STD. All the new stuff then becomes templated.
All a massive fuckup.
You need to have strongly applied coding rules, not just syntax but on the language and libraries used.
The module needs needs to be frozen to that C++ version.
End of the day, I spend more time testing.checking stuff than I do writing new stuff. Any language that makes testing easier gets my vote.