Get singular or Plural string with regex in Java

I want to replace a variabel in a String to a singular/plural word based on a number.

I've tried to use regex, but I don't know how to use a combination of regex and replaces.

//INPUTS: count = 2; variable = "Some text with 2 %SINGMULTI:number:numbers%!"
public static String singmultiVAR(int count, String input) {
    if (!input.contains("SINGMULTI")) {
        return null;
    }

    Matcher m = Pattern.compile("\\%(.*?)\\%", Pattern.CASE_INSENSITIVE).matcher(input);
    if (!m.find()) {
        throw new IllegalArgumentException("Invalid input!");
    }

    String varia = m.group(1);

    String[] varsplitted = varia.split(":");

    return count == 1 ? varsplitted[1] : varsplitted[2];
}
//OUTPUTS: The input but then with the SINGMULTI variable replaced.

It now only outputs the variable, but not the whole input. How do I need to add that to the code?

You can use Matche's replaceAll method to replace the matched string.

In fact, you don't have to split the string, you can just match for the : in your regex:

// You don't need the "if (!input.contains("SINGMULTI"))" check either!
Matcher m = Pattern.compile("\\%SINGMULTI:(.*?):(.*?)\\%").matcher(input);

If the count is 1, replace with group 1, otherwise replace with group 2:

// after checking m.find()
return m.replaceAll(count == 1 ? "$1" : "$2");