Selected approach working fine for latin characters, with case insensitive option:

val lat = "udf".replaceAll("(?i)\bUDF\b","")
println(lat)

This function matches “UDF” and returns empty, as I expected.

But this one:

 val cyr = "ая".replaceAll("(?i)\bАЯ\b"," ")
 println(cyr)

returns “ая”, so it does not match word in upper case.

I there any way to solve this task?