Please remember English is a very new language, relatively speaking, only about 700 years old only and constantly evolving. In that time many different dialects and usuages have evolved and people within the original island of Great Britain can have difficulty understanding "English" as spoken by other groups. Geographical distance resulted in varying uses of English in North America, India (Hinglish), Australia (Strine)often virtually unintelligible to some of the original English speakers. This is what happened to Latin which degenerated into multiple languages as the Roman Empire died, many of these cannot be understood by the average person who speaks French, Italian, Spanish, Portuguese, Catalan etc.
The hope is that with the internet and modern comms that an internationally agreed system will arise. But when English people in England have changed their everyday use of English by dropping the T in words like Sco-land and omitting the R sound in words like number Pronounced Numbah, who can teach who 'ow to talk proper?