My family have actually had two unpleasant experiences with this recently. My Dad was in hospital and he suffers with MS, so physically he is doddery but mentally he is all there. All the nurses in his hospital were Philippino and unless directly addressing a patient spoke their language to each other at all times. When discussing how they were going to lift him, when talking about his treatment plan. It was really unpleasant for ALL the patients concerned, whether English/British or not. English was the common language of nearly all the patients, sometimes it was very clear that the nurses were discussing patients in their own language, even seeming to laugh at them and it made a lot of the patients uncomfortable.
My Gran had a similar experience a few months ago, she went to an eye doctor, he took her for an appointment into another room where two other men were. He never introduced the men to her or told her who they were. Yet he repeatedly turned round to him and discussed my Gran's case with him in Arabic.
It's unfair as it puts patients at a disadvantage and doesn't allow them to be fully informed and make decisions about their care properly.
I also think it's an issue because talking in a language which is not local can be used as a means of workplace bullying and exclusion, which I believe Amazon UK previously complained about. I've heard of that method being used on building sites in the past in order to drive workers who are not Polish/Romanian/Bulgarian whatever out and secure the job for a mate from their native country.
And to be honest it's just plain rude. It's acceptable to talk to a customer or a client in their native language if that makes things easier for them because they are the customer. But for colleagues to chat between themselves in their own language in the earshot of others is just plain rude.