Which language should I speak?

Working in a diverse environment with team members from many nationalities is a great experience. You get to know new cultures and recognize how similar people are across the world although the seemingly extreme differences.

In such an environment, you hear different languages all the time! And although there is usually a de facto business language, -English in my case, since I'm currently working in Australia-, some people prefer to have conversations in their native tongue with colleagues that share the same language even in a business context.

Well, is that OK?

There are many angles from which I see this matter.

It's good to feel natural

As a non-native English speaker myself, I feel very weird speaking with my Arabic speaking colleagues -especially Egyptians- in a secondary language, it just doesn't feel natural! Why speak in a language that we wouldn't normally use if we were having a casual chat? Put aside losing access to a huge stock of vocabulary and expressions that we share. This leads to the second point:

It's about effective communication

We need to get the job done, right? So why put a barrier in front of effective communication? Undoubtedly using my native language makes conveying my thoughts much easier. Besides, it gives better control over the tone of the conversation. I suppose the same goes for other nationalities as well.

But what are we missing?

Some people might feel excluded when others around them speak in a language they don't understand. However, I haven't seen this causing real issues.

A virtual wall?

I've been working in Agile teams for years. And I believe in the value of having collocated teams in facilitating communication. 

It happened many times that I overheard a discussion between other colleagues in my team area when I jumped in and gave help to solve an issue, guided on a topic, or threw in a piece of information that was necessary to solve a problem. Even if you're not intentionally paying attention, it's possible to save the team from consuming a lot of time going in circles.

Speaking in a different language defies the purpose of collocation and creates virtual walls. It's the same reason why some Agile practitioners recommend not putting headphones as they isolate the team member from the surrounding team interactions.

What about you? Do you prefer speaking in your first language if different from the common one used at work? On the other side, how do you feel about other colleagues speaking in a language that you don't understand?