If I understand it correctly they have DNS servers spread out at different locations. These locations are also BGP peering locations. If the DNS server at a location cannot reach the other datacenters via the backbone it stops advertising their IP prefixes. The hope is that traffic will then instead get routed to some other facebook location that is still operational.
Well, as someone who has taught different languages as first, second and third languages to students and young pupils I would say it becomes easier. Not easy in an absolute sense. It still requires effort.
I would however agree with you that those who say "it's easy to learn another" in an absolute way has usually only considered languages from the same group so far.
Not sure how to write this. I am hoping the next level of fluff to be removed will be implementing concrete algorithms in procedural or functional style in day to day coding. Instead we should be leveraging other programs (such as SMT solvers, but not limited to those) to produce a suitable implementations of solutions.
That is, we should try to focus more on specifications, in one form or another.
So much of the software I work with could plausibly have been written by a machine instead.