using System;
using System.Text.RegularExpressions;
public class Test
{
    public static void Main()
    {   
        string msg= "array1[ array2[array3[1,1],3] , 5+3 ]";
        var charSetOccurences = new Regex(@"array\d*\[\s*((?:[^\[\]]|(?<o>\[)|(?<-o>\]))+(?(o)(?!))),\s*((?:[^\[\]]|(?<o>\[)|(?<-o>\]))+(?(o)(?!)))\]");
        var charSetMatches = charSetOccurences.Matches(msg);
        foreach (Match match in charSetMatches)
        {
            Console.WriteLine(match.Groups[1].Value);
            Console.WriteLine(match.Groups[2].Value);
        }
    }
}

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