For non-native English speakers these sounds might be very difficult to be learnt. There’re 2 standard sounds represented by the letters “th” in English.
And there is no way out: you can’t replace them with sounds you consider ”alike”. They’re unique sounds and once you learn them you – and others – will notice a watershed in your English pronunciation ability.
When travelling for instance, people may not understand if you pronounce “three” and “tree” the same; they might get what you’re saying from the context but still, this kind of mistake definitely affects the quality of the communication.
Let’s dive into it, shall we?