The differences in writing between British and United States English are small. Apart from minor spelling, vocabulary and punctuation differences, written English is essentially the same worldwide. For example, Canadian English shares some of the features of British English and US English; Australian, New Zealand, Irish and South African English generally follow British English spelling with minor vocabulary differences.
Similarly, differences in speech should not be exaggerated: there is greater variation in spoken English between London and Glasgow than between London, San Francisco, Cape Town or Sydney.
The PhraseBook has been written very much with international use in mind, and suggests ways to make your writing standard worldwide, avoiding national shibboleths. British and US alternatives are marked throughout the PhraseBook, and differences in spelling, vocabulary and punctuation are outlined in the relevant Writing Help sections. All other words and phrases in the PhraseBook can be used without restriction.