kein = nicht ein So when you negate an noun, it depends on the kind of article (definite, indefinite, none) if you use "kein" or "nicht". "Ich spreche kein Deutsch" is also correct. "Ich bin nicht Engländer" sounds a bit strange, because one would expect an indefinite article, as in "Ich bin ein Engländer" (= it's a defining quality that I am from England). If you replace "Engländer" with a word that doesn't need an article, e.g. an adverb, "nicht" is fine: "Ich bin nicht groß".

German's not my mother tongue, but here's how I understand it. 'Kein' is like 'no' in English, and can be used before a noun to negate it. Just don't mix it with 'nein', which is used to answer questions. 'Nicht' negates a verb. It's like 'not' in English, except that in English 'not' can only be used auxiliary verbs. Ex. "Ich bin keinen Engländer" is like "I am no Englishman." "Ich bin nicht einen Engländer" is like "I am not an Englishman". In English they mean the same thing, except "I am no..." is a lot more emphatic. I'm sorry to say I don't know if such a difference exists in German. I also don't know if both of them sound natural.