Yes.
The letter 'Z' is still a fully used, fully functioning letter of the English Language.
NO ! Chinese, Spanish, Arabic, and others are still widely used ( though English is popular)
"Wuu2" is a text abbreviation commonly used in English-speaking countries, so you would still refer to it as English.
is English the language commonly used in Vietnam
The most used vowel in the English language is the letter "e."
The most frequently used language on the net after English is Chinese.
The English language is used more in Ireland the Irish language is used only in some certain areas but the English is definettely used more, the children in Ireland tend to learn the Irish language in school.
English is their main language.
Well, not to be rude but there is a mistake in your question, instead of just mistake, it would be mistakes because it is plural. The most common mistake I think in the English language is sheeps and fishes. The plural is sheep and fish. But when you are referring to multiple kinds of fish the word fishes can be used. Another one is octopuses and cactuses. This would be cacti and octapi. Although, octapouses is getting more and more comon and now is somewhat grammatically correct.
The English language is written using the Latin alphabet.
English is the most spoken language in the world and used for communication.
Two words borrowed from the Spanish language and used in English are "quesadilla" and "fiesta."