This is not helpful advice at all. First, it's rather lopsided. You make it seem that "American English" is not really "English." And, you ignore the differences in other countries for spelling, pronunciation, and word use – such variances exist, for example, in Austrailian Oxford Dictionary (for Australian English) speakers, Dictionary of South African English (South African English speakers), and The New Zealand Oxford Dictionary (for New Zealand English speakers), to name a few. There are such difference even in Scotland's Scottish National Dictionary and Ireland's Irish English Dictionary.

Moreover, if you're in America and use what you call "English" instead of "American English" spellings in academic settings, your work will be marked incorrect. I know this for a fact because I always read a lot and much of my reading was by UK authors. So, in school, when I used words I thought I knew how to spell from those UK English books, those words were marked as incorrect in all of my US schools – even when writing literature lessons on Shakespeare or Byron.