Reasons for using the same word for people and language of a country?

(Note: I actually wanted to post this as a comment, not an answer, but for some reason it doesn't seem to do anything when I try—simply does not react.)

FJDU, you are missing the fact that in Chinese, you do not really say English language/people, since Chinese does not have a way of morphologically deriving adjectives from nouns. What you really say is England language and England people. Different languages derive words from each other in different ways; in English, an adjective can be derived from country (and similar) names, and these adjectives can then, like so many other, be used as nouns. If you simply make a noun out of an adjective that means ‘of England’, it makes sense that that will most often refer to either the people of England or the language of England.

There are languages where simple adjectives, nouns for people, and nouns for languages have three different forms (Irish and Scottish Gaelic work like this, and I have some vague memory of reading somewhere that Turkish does too?); there are languages where two are the same and one is different (English is partly one of these, at least for some languages/countries; Germanic languages in general share the same distribution of adjective + language being the same and people being a different word; Finnish has a slightly different model where adjective + people are the same word, but language is simply the name of the country/place itself, underived); and there are languages where all three are the same (such as Chinese).

There is no real ‘reason’ as such for all this. It is just part of what makes languages different from each other.

It's often frustrating to ask 'why is it this way' in any language. The most common answer is 'it's that way just because that's the way it is' :)

In English, though, part of the answer to your question is that we can tell from context whether you're referring to an English person or the English language.

For example, if I say 'He is English', you would know that I'm not talking about the language because a person cannot be a language.

Likewise, if I say 'She speaks English', you would know that I'm not talking about an English person, because a person cannot be spoken.

So context is the key. That's how we know the difference. As to 'why', well, that's just the way it is :)

By the way, in French the same phenomenon occurs: a 'French person' is a 'français', and the language is also 'français'. Also in French, an English person is an 'anglais', and the language is also 'anglais'. I suspect it is like this in many other Romantic languages. And you can tell the difference from context.