As a native English speaker who has done some fairly extensive travelling, I've realised the advantages I've had when it comes to understanding the many different "flavours" of English that exist.
I often take for granted that I understand "schedule" is pronounced "SKEH-djule" or "SHEH-djule", depending on where you're from. I am fully aware that "chips" could also be confused with "crisps", and "a-LU-mi-num" is also "al-u-MIN-e-um". And, has anyone besides my MS Word dictionary even noticed that I'm using UK spelling and grammar?
These kinds of differences in English are things I just write-off to different cultures and ways of learning, but for Thai students, from whom I all-too-often hear that London is the capitol of America (not even the US... read: culturally unaware), national/regional English differences make something that's already quite complicated... well, ridiculous.
I've found this to be especially difficult for private and/or corporate students in Thailand, as they often enroll in multiple sections of 20/30/40 hour courses that each have different instructors and course materials. "But teacher, my last teacher said ‘tomAHto', and you say ‘toMAto', so who is right?" From the standpoint of someone trying [well... lazily trying] to learn Thai from different people who pronounce the same things differently, I can completely understand the problem. What is there to do?
Pronunciation exacerbated, overall accents are another biggie. Amusingly to me, in my experience most Thai public schools and language centers gravitate towards British English textbooks, focusing on UK grammar and spelling. Yet, often, when a teacher pronounces a word with a British accent, the students respond with a blank stare. Repeat the word again, trying to sound like Brad Pitt, and bingo! The eagle has landed.
To be fair, many Americans (of which I must admit I am, for better or worse) I know have no idea what someone with a thick Brummie or Scottish accent is saying either; I often forget that I'm an oddball in that my favorite TV shows include Are You Being Served, Yes Minister, and Black Adder, among many other British comedies, and allowing me to be exposed to many of these regional accents and/or dialects. What can I say, I'm a sucker for old Brit Coms.
Whereas Americans at least share the same general language and vocabulary, my Thai students often have quite a hard if not impossible time understanding accents that are different than those they are accustomed to; Thai focuses far more on a mainstream pronunciation than English due to its tones, and listening for multiple pronunciations of the same word is no easy feat. I've given up watching Sherlock and Top Gear with my Thai girlfriend without subtitles.
I always try to draw attention to the differences in UK versus US peculiarities (and I'm generalising here-all native English varieties) as they arise in classes. My explanation is typically something positive along the lines of, that's the cool yet confusing thing about English; there are many "correct" ways to pronounce and write English. Unless someone has chosen for you [as is often the case here], just pick one way and go for it!