[ashishb]

> My personal theory is that this is because you can make every sound you hear in English using the Devnagari script, but not the other way around.

Not true. There are phonemes which are similar but distinct.

For example

  -  `v and w` map to the same thing in Hindi
  - th and थ are allophones but different sounds

https://ashishb.net/linguistics/hindi-english-phonemes-that-...

Hindi written in Devanagari is highly phonetic (not perfect but near perfect). However, English is not phonetic at all. E.g., "Th" in Then is different from the "Th" sound in Father.

[devilbunny]

We must be using different forms of English, then, because they sound the same to me. “Thin” and “then” do not.

[umeshunni]

Indeed.

In US pronunciation, Then is ðɛn and Father is ˈfɑðɚ.

In UK (received), Then is ðɛn and Father is ˈfɑːðə(ɹ).

In Indian English, Then is ðɛn and Father is ˈfɑːd̪ə(r)

[ashishb]

Sorry I meant think and not then.