The thing about a language being "a dialect with an army" is a bit tongue in cheek. Of course we'd like more consistent ways to distinguish languages that don't

The thing about a language being "a dialect with an army" is a bit tongue in cheek. Of course we'd like more consistent ways to distinguish languages that don't depend on politics. When there's a continuum (like the Scandinavian languages) and it's hard to decide where to draw the arbitrary line, national borders are a pretty convenient place to settle on. But that's not so fundamental that it "doesn't make sense" to ask why we distinguish languages. It's easy to imagine Norwegian and Swedish being considered the same language if they were the same country. It'd be a language with multiple written forms, but Norwegian already has two of those anyway. But you can only get so far by simplifying the issue to say that language borders are national borders. That erases a lot of the linguistic complexity of Europe, it defies reality in Africa and South Asia, and it just wouldn't make sense at all in North America. (What's the Canadian language, besides a joke on South Park?)