This question already has an answer here:
I work in a small company in a country where the national language is English, and the majority of developers only speak English, recently three developers were teamed up to work on a feature, two of those developers share a first language that is not English (A, B), the other only speaks English (C).
Developer A worked on the API whilst developers B and C worked on the app. During the development of the feature, developers A and B had extensive technical discussions in their native language, only switching back to English to ask questions to other developers.
In our office it is common that other developers listen in to technical discussions and offer input on certain decisions that are being made, this quite often finds pitfalls in ideas before they get anywhere near implementation and saves quite a lot of time.
Developer C has expressed that he found working on the feature especially hard as he quite often did not find out about choices that had been made, until after they had been implemented and had no opportunity to shape these choices.
What I am asking is that is it appropriate to enforce that all technical discussions be carried out in the national language.
This is not the same as the one it has been marked a duplicate of, as it would be unreasonable for all employees to learn the languages of only some of the staff.