let's take USA for example, American English in Mid-western is considered standard (i.e. newscasters speak mid-western because it has no accent)....

Firstly, I think you cannot compare chinese and english. Chinese is not a language, it´s a family of languages. Mandarin is not standart chinese but the official and national language of China. Although other languages like cantonese, shanghainese, etc. are called in China "dialects" they are completely different languages and not dialects in a linguistic point of view. English has regional variations but is still one language. Every language has social and regional variations in vocabulary and pronounciation, the concept of "standard" language is based on political criterions, the most important and richer regions will impose their variety as "standard". For example, standard french is the french spoken in Paris because it´s the capital and most important city. Linguistically it doesn´t exist a "standard" language, every language change creating regional varieties, with time these changes will create different dialects and even complete different languages, originating a new language family as it happened with latin that split in many romanic languages.

In Britain there used to be RP (Received Pronunciation) and the BBC had a 'pronunciation Unit,' but there are many variations in accent and dialect and the language is changing all the time. People still talk about 'The Queen's English,' but i think there is no true Standard English now.

It's difficult to say where there is "standard" English. For example, in the United States many varieties of English exist, and the "standard" is only an ideal. In China, the national language is spoken with many accents. Some people like to say "standard" Mandarin is spoken in the Northeast. Who says so?