The first is to deal with the challenges of multilingualism beforehand and also to admit your own lack of expertise and not just think, “It’ll work out, everyone knows English.” Unfortunately, when it comes to language, everyone thinks they have a say pretty quickly, but de facto, trained staff and preparation for the challenge are the keys to success.
Second: Realize that multilingual communication with each other means more time and it will certainly reduce team productivity in the beginning before the desired synergies kick in.
Thirdly, to be familiar with the CEFR (Common European Framework of Reference for Languages) in the European area, at least in the field of levels, as well as with the common examinations such as B2 for the professional, C1 etc. The still often used terms “business fluent, fluent, native speaker” are too vague and poorly measurable.