[_emacsomancer_]

> Japanese has significant vowel length, which English doesn't. In Japanese, "un" means "yes", and "uun" means "no". Imagine if "yes" and "yesssss" meant opposite things in English.

That's sort of true, but you also have to realise that English underwent a sound change that changed the purely quantitative (vowel length) distinction into a qualitative one, changing Middle English long vowels into diphthongs. [And for things that sound very similar but where one means 'yes' and one means 'no', think about English 'un-huh' ( https://en.wiktionary.org/wiki/uh-huh#English ) and 'unh-uh' ( https://en.wiktionary.org/wiki/uh-uh#English ). See the links for both audio files and IPA transcription.]

That just means in modern English vowel length isn't distinctive, but it is in Japanese. English on the other hand has a distinction between /r/ and /l/ that Japanese doesn't ( https://en.wikipedia.org/wiki/Perception_of_English_/r/_and_... ).

In other languages (like Tamil), voicing distinctions in stops aren't phonemic (so 'log' and 'lock' would be non-distinct). And so on.

If as a non-native English speaker you produced 'rog' when your intended meaning was "lock", people would stare at you in confusion too.