Here are some possible interpretations:
* "I'm fine" or "I'm good": If someone asks you how you are, you could respond with "nalla yennai."
* "I'm good at it" or "I'm good with that": If someone asks if you can do something, you could use "nalla yennai" to indicate you're capable.
* "I'm a good person": In a more general sense, "nalla yennai" could be used to express that you are a good person.
To get a more accurate translation, you need more context. For example, if you were to provide the full sentence or a brief description of the situation, I could give you a more precise translation.