I believe that your inquiry is to figure out a good topic for research that would include ALL English speakers from every country that speaks English. If this is the case, the first thing to consider is what is your main curiosity about people who speak the English language. Analyze this from several perspectives:
Historical - ideas
- how has the English language usage grown/decreased from (year ____ to year ___) or from the ___ century to the ____ century.
- how has English been adopted in the countries where it is spoken
- what needs have led some countries to adopt English as a language, or learn it as a 2nd language.
- How did the EL spread throughout the old world and the new world (or you can study the separately)
Linguistic - ideas
- phonological differences between English from England and English from Ireland.
- differences between EL spoken in Europe versus EL spoken in North America.
- Is it best to teach English as a whole language or phonetically?
- English language literature: differences and similarities between American and British literature.
- How does book ____________ represent the average citizen (focus on specific countries where such citizens are from)
Whichever topic you chose, remember that English is used as a 1st language in many countries but in other countries it is used as a 2nd language just as fluently as a 1st language. In other countries English could be learned for specific purposes (LSP) or for mere technical usage. Therefore, do not focus so much in the "English speaking population" because you will end up writing a book. Focus on a population of a specific country or two specific countries and choose which comparison or research you wish to conduct. In other words, establish parameters and limitations so that you keep the focus.