Thanks for your condolences. My uncle suffered for a long time too, and the last two weeks were unbearable.
We don't deal with foreign customers directly, but we do get customers (particularly from Puerto Rico) that have thick accents or have difficulty making themselves understood. The short answer is that you just have to take your time and go more slowly than you normally would with a more cogent English speaker. Break a call down into as many individual parts as necessary. Give it extra effort. The problem is a combination of both, but more the former I think.
Hope this helps!