This is entirely true, but it's also worth mentioning that English varies more than it gets credit for, too. Plenty of vocabulary, expressions, and even grammar

This is entirely true, but it's also worth mentioning that English varies more than it gets credit for, too. Plenty of vocabulary, expressions, and even grammar differ by dialect, and if one isn't making an effort to speak in standard English a fair bit of what they say won't be understood by the whole anglosphere.