The "most Kotlin-esque" way I found to do this sort of formatting is:

"%,.2f".format(Locale.GERMAN, 1234.5678)      // => "1.234,57"
"%,.2f".format(Locale.ENGLISH, 1234.5678)     // => "1,234.57"

"%,.2f".format(1234.5678)                     // => "1,234.57" for me, in en_AU

Note though that even though this is Kotlin's own extension method on String, it still only works on the JVM.

For those looking for a multiplatform implementation (as I was), mp_stools is one option.

As a workaround, There is a Kotlin stdlib function that can be used in a nice way and fully compatible with Java's String format (it's only a wrapper around Java's String.format())

See Kotlin's documentation

Your code would be:

val pi = 3.14159265358979323
val s = "pi = %.2f".format(pi)

I know some of the above solutions work perfectly but I want to add another solution that uses ceil and floor concept, which I think is optimized for all the cases.

If you want the highest value of the 2 digits after decimal use below code.

import java.math.BigDecimal 
import java.math.RoundingMode
import java.text.DecimalFormat

here, 1.45678 = 1.46

fun roundOffDecimal(number: Double): Double? {
    val df = DecimalFormat("#.##")
    df.roundingMode = RoundingMode.CEILING
    return df.format(number).toDouble()
}

If you want the lowest value of the 2 digits after decimal use below code.

here, 1.45678 = 1.45

fun roundOffDecimal(number: Double): Double? {
    val df = DecimalFormat("#.##")
    df.roundingMode = RoundingMode.FLOOR
    return df.format(number).toDouble()
}

Here a list of all available flags: CEILING, DOWN, FLOOR, HALF_DOWN, HALF_EVEN, HALF_UP, UNNECESSARY, UP

The detailed information is given in docs

For Displaying digit upto two decimal places there are two possibilities - 1) Firstly, you only want to display decimal digits if it's there. For example - i) 12.10 to be displayed as 12.1, ii) 12.00 to be displayed as 12. Then use-

DecimalFormat formater = new DecimalFormat("#.##"); 

2) Secondly, you want to display decimal digits irrespective of decimal present For example -i) 12.10 to be displayed as 12.10. ii) 12 to be displayed as 12.00.Then use-

DecimalFormat formater = new DecimalFormat("0.00");