The unification of countries and nations into the Planetary Union brings the urgency of a unified written and spoken planetary language that allows for easy and undisturbed communication and a more constructive cooperation. This doesn’t mean using the language of the most developed and populous nation but a language that is determined by linguistic experts.
What about all those old established languages that were used for centuries and even millenniums? They still remain in usage but as secondary languages. The society and people alone take care of their preservation and by doing so, they continue to enrich the cultural diversity of the ecohumanist society.