The level of interaction skills and networking clue required to work
effectively at the IETF is considerable. (And yet many people manage it,
including newcomers, students, and specialists on some specific aspect.)
But language is just one aspect of the ability to interact with others. We see
some failures in communicating due to language. However, in my personal
experience some of the other aspects are more important. Ability to make a
topic understood, presentation skills, ability to use evidence and logical
arguments, capabilities in building groups that work together on a problem, and
so on.
Jari