Some Anglophone Nations 

United Kingdom

On your first visit to the USA from the UK, you will probably think there will not be a language barrier and largely you shall be correct: an American can certainly read 98% of what you write down. With speech, it can be harder: the standard accents for America and Great Britain diverged sometime in the late 17th century and have remained on different courses ever since, plus the U.S. has been more consistently bombarded with influences from other tongues brought by immigrants since birth and continuing to the present. There will be idioms and ways of speech that will baffle and amaze both sides in any conversation.

If you travel to some of the tourist hot spots - like Florida or New York City - you will be one of a million tourists and should have no problem. In other places, like the Midwest, Rockies, and portions of the South, you may need to speak more slowly than at home, especially if you make your home outside Southern England.  The reason is that the accents found in these areas of England are what Americans associate most with the UK owing to the fact that these are the ones that have been featured in film, television, newscasts, and theatre for over a hundred years on both sides of the Atlantic; both the BBC and American media market have featured these accents for far longer than the others (Brideshead Revisted and Simon Cowell have not helped, and in fact the truth that most actors that appear in films exported to the US do not feature a very broad range of accents-the 3 principal characters from Harry Potter, for example, speak with a bog standard middle to upper class London accent.) Whereas this has been changing in America for the last 20-30 years, bear in mind it is just as frustrating for them to understand you as it is for you to be understood.

What you sound like

To American ears there are accents that *may* place a person as from the UK. However, the vast majority of Americans will have no clue where somebody is from in the UK, with the most confusion centering around England. Indeed, many Americans cannot tell the difference between an English, Australian, New Zealand, or South African accent!  A Scottish accent is more easily identified but still may leave some folks puzzled. To the average American, a Welsh accent is just confusing. Northern Ireland sounds like Irish from the Republic but with idioms closer to the rest of the UK.

What to do

It helps Americans understand you if you speak more slowly and don't use slang that is not common in the USA.  If you are having a difficult time being understood, try remembering what Tobey Maguire sounds like and imitiate him, and pay attention to where he puts his r's : Maguire was born and raised in California and this is an accent often heard on American TV and especially in movies.  He is the best match as it is easiest for everyone to understand.  Most Americans will expect you to sound like Simon Cowell, Piers Morgan or Sharon Osborne ... but even if you don't, they will try hard to understand your accent. (They've been trying hard to understand Ozzy Osbourne for years.)

Republic of Ireland 

Congratulations! You are from a country that has exerted enormous influence on American politics, literature, and people: one U.S. citizen in five can trace his or her roots back to Ireland, some (particularly in New York and Massachusetts) with parents, grandparents, and great-grandparents either living within Ireland still or having emigrated as recently as the 1980's.  You have a brogue that will make Americans think "Irish! Definitely Irish!". You will, however, encounter some barriers similar to your UK counterpart above, mainly with idioms.

Just because 20% of Americans trace their lineage back to Ireland, do not assume this is evenly distributed throughout the USA - it's not. The Northeast has the greatest concentration of Irish descendants but if you visit Utah, Louisiana or many other states you may get a blank look after telling somebody where you live!

 What you sound like

Your accent sounds unique to any of your immediate geographical neighbours, and to some Americans in the northeast USA you sound "just like great-aunt Moira."   You prononce the letter "r" much like most Americans do:  "Parking garage?" will be easily heard and answered with "Five blocks down, Ma'am."  However,  you tend to speak faster than most Americans can understand what you are saying-SLOW DOWN!  The goal is to be understood, not to hop up and down in frustration and shout when you aren't and consequently possibly speaking even faster. (The same problem, alas, is what Aunt Moira was remembered for.)

What to do

Idiomatic speech is clearly different in America, and although you get a steady diet of theirs they may not know all of yours yet: if you tell a shopgirl the dress is to "tarty" she most likely won't have a clue what you mean!  (Tarts are exclusively food, not people.)  Similarly, a sign in Disney World might say "fanny packs: $25 each."  It means they are selling a pouch like contraption that fits below the navel and fastens around the back with two nylon straps (eg, similar to a moneybelt.)  They are also called hip packs or waist packs. It has nothing at all to do with Mum's privates and would be rather odd if it did as plenty of Dads are wearing them on the way to Pirates of the Caribbean with the camera inside. 


Australia and New Zealand

You have survived the incredibly long flight to Los Angeles or the even longer flights to points elsewhere in America: for this, you deserve a medal let alone a good place to lie down and adjust to crossing multiple time zones. Some of the time you will be recognized for sounding like Steve Irwin, Hugh Jackman, or Paul Hogan.

What you sound like

Australia and New Zealand sound extremely, uncannily, and maddeningly similar to American ears - it is similar to how some have trouble telling the difference between a Canadian and American accent.  A few Yanks have accidentally provoked anger and misunderstandings for mistaking a Kiwi for an Aussie: it is totally unintentional and rarely meant to cause offense.

An American may eventually be able to pick an Australian out because Australian slang uses more diminutives, especially ending in -ie.

Americans cannot tell that an individual is a Kiwi the way Australians can when they hear 'fish and chips' being pronounced as 'fush and chups.'

What to do

New Zealanders, do not get too angry if you are mistaken for your neighbours: it is NEVER meant to hurt your feelings and more likely mentioning Whale Rider or Lord of the Rings will help you point out you are definitely NOT from Australia. (If you speak any Maori, this will make you very popular in Hawaii amongst those with Hawaiian heritage or on college campuses: it is a related tongue.) 

Australians, try to curb using diminutives too often as it may be confusing; some may think you are looking for a small or very young version of whatever something is. An exception to this rule is the word "barbie", owing to some commercials Paul Hogan made many years ago. Americans do know what a "barbie" is, but 99.9% won't have a clue what an "eskie" is.

In short, be aware that many Americans may have a hard time understanding your accent . . . and you may have a hard time understanding theirs! Take your time, don't use slang and enjoy your holiday!

Before One's Trip buy "Speak American" or a Similar Book:  Check for this title on Amazon, there are several others.  "Speak American" is a very good overall introduction not only to standard American usage and slang across the country but also to many customs and necessary information about daily life and manners.  The "Speak American" book was most helpful to colleagues who were seconded for long periods of time from the UK and France to the United States.