Thanks for following this. The thing was that we all spoke *very* slowly and clearly. If you had read my post with care, you would have noticed that I even translated the English questions into Mandarin, they answered in Mandarin and then I asked them to repeat in English. Well, most of cases, it was silent.
I'll send another post after interviewing another candidate next week. Hopefully, he can talk to us.
To your example of Spanish, I'm sure those who take Spanish lessons in primary and secondary schools won't have any problem to communicate with any Hispanic engineers. I don't have examples for Spanish but I do know quite a few taking on German or French with ease.
By the way, I never heard of "London accent". There are so many accents in London. The most famous is Cockney of the East Enders.
