It's brilliant if your flight deck mate can perform PA's in multiple languages, can be bloody useful sorting pax issues out and can add hugely to the operation as a consequence.
If your non-UK mate chats to his/her mates at any time and you don't understand it then so what. We Brits can be so cryptically insulting in our own tongue anyway.
What is relevant and important here is that your colleague who is working for a UK AOC MAINTAINS and COMPLETELY COMPREHENDS to a high standard the English Spoken Language. This is so we can work out what the problem is, generate options and deal with it effectively. SOP 'grunting' is the easy part and a robot can do it.