The document discusses varieties of English across different geographical locations and social groups. It explains that while Spanish does not vary much within a country, English changes significantly depending on factors like location and social class. This variability is interesting for language teaching as it applies to all languages. Students of foreign languages need to be aware that English differs worldwide and dialects can sound like different languages to non-native speakers. Understanding this variability may help avoid embarrassment when speaking to English speakers from different countries in the future. The text also briefly discusses the history of how English dialects developed from migration and conquest.