国际民航组织没有规定普通话是官方认可的飞行语言。 但他们确实规定英语是正式用语了！
The international civil aviation organization doesn"t mandate that Mandarin be the official international language of aviation. They do however, mandate that English is the official language."
正式语体是你在教科书、参考书和商务信函中看到的用语。
Formal language is the kind of language you find in textbooks, reference books and in business letters.
“语域”是一个术语，通常用以描述语言中用语的正式程度。
'Register' is the term commonly used to describe different levels of formality in language.
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