Standard English is essential for most senior posts. It is the variety of English expected of people with power and influence and so on.
Standard English is the literary dialect. It is not "bad."
A dialect is ungrammatical because it differs from Standard English in grammar and usage. Some dialects deviate far from Standard English.
Formal English is THE standard English. This is in oppsoition to informal English which is spoken English and includes slang and colloquialisms.
The most widely understood English dialect
Standard american english
Standard English is the literary dialect, which everyone understands even if they don't speak it at home.
"Sykes, why did you throw that whip on me like that?" is the best translation into Standard English of this piece of dialect.
Standard American English.
Trualse
"Standard English" is the literary dialect used in formal writing and in the speech of well educated persons. It descends from the West Saxon dialect of Old English, specifically the dialect of London. "Non-standard English" includes many regional dialects, whose grammatical forms and words ( such as ain't and varmint, for example) are not exactly incorrect but are unsuited to formal discourse; and the non-regional dialect known as Black English ( or Ebonics ) which has a prominent substrate of African grammar. There is another literary dialect called Scots ( or Lallands or Doric ) which is considered non-standard because descends from the Anglic dialect of Old English, not the Saxon.
English is not "based" on any other language. Standard English is the surviving form of the Saxon dialect of Old English; Scots, also called Lallands or Doric, is the surviving form of the Anglic dialect.
Hardly. There are many forms of non-Standard English, and they all have far more limited vocabularies than Standard English - which is the literary dialect, after all.