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What is RP and GA?

RP is Received Pronunciation. It is often called Standard British English.  Unfortunately many call it snobbish, which it is not (my humble opinion). It is a very neutral accent, but very clear and precise
GA is General american.

How about German standard English with some bits of Singlish thrown in - also can what?

) Well, there is no German Standard English as such. I mean technically speaking. But of course, one can mix languages. The so called intolerant native speakers would shout blue murder. Only geniuses like Prof. David Crystal (the most world famous linguist from Cambridge) accepts the term "global English". All the others are not tolerant of the dynamics of language. (I know I shall draw (destructive) criticism here, but that is "OK" by me.

I like the world's various "bazaar" languages like Suaheli, Malay, Creole, Pidgin and other corruptions of English. They are easy, flexible, inclusive (of other language bits as well as non-native speakers) and convey an "anything goes" attitude.
It is seldom advisable to be dogmatic - be it about language, religion, lifestyle, morals, etc.!

As a multilingual person myself, I am flexible. I do admit a liking for RP and standard English, but I do not make other forms of English bad. However, the native speaker cliche has created a difficulty in the field of employment.
When it comes to the regular use of the language, I am open to all forms, because I accept the dynamic nature of English.