Why English is ultimately so hard to master

'English is the easiest language to speak badly and the hardest to master'

This phrase is undoubtedly untrue, yet I believe it has some truth in it. I've thought about it, and I think it has something to do with this.

If someone who has a sound understanding of grammatical concepts, was to study both English and German for say five years, without having much exposure to the way each language was actually spoken, the learner of German would probably produce German that would be considered more accurate and less weird sounding than the learner of English. They would follow the rules they had learnt and produce sentences, that while sometimes stilted sounding and lacking the little interjections, would mainly sound ok to a German speaker. The learner of English, meanwhile, would probably produce sentences, that while not particularly grammatically incorrect, would somehow sound way off a lot of the time.

To make yourself understood, you don't have to learn much English grammar as an E2L student. Just string a few words together in approximately the right order, and we can get usually the gist of what you're saying. I don't know if that's true most other languages.

Aren't all languages very hard to master (i.e. speak just like natives, with no hint of foreign accent)?

BTW, I've heard that German is worse morphologically, has more complex syntax, and also more irregularities than English. Perhaps the German spelling is better, though.

I'm not sure you understood the question. Yes, German is morphologically much more complex. That's why I asked about someone with a sound understanding of grammar. I think if such a person learnt all the grammatical rules in German and English, without any real exposure to the way both languages are spoken, the person following the rules in German, although more complex, would produce more accurate sounding language than the person studying English. I think that's because studying formal grammar rules will get you much further with a language like German, whereas with a language like English, you simply have to hear it, because while it lacks formal grammar, there are more funny rules about how words can be used together.

I disagree. I've learnt English and Finnish and if often find that by strictly following the rules of grammar I tend to produce sentences which, while grammatically correct, are completely bizarre to native speakers. I often end up working painstakingly through the complex morphologies, only to my dismay, to find that a native speaker would actually say it in a MUCH simpler completely different way. For more technical styled language I have more success but informal every day language you MUST get used to the idiosynchrasities of native speakers just by exposure just like English. In synthetic languages just as in English, many things are grammatically correct but simply not how things are said.