Some common extensions used over the years in some revision or another

StringExtentions.cs

using System;
using System.Collections.Generic;
using System.Globalization;
using System.Text.RegularExpressions;

namespace Extensions
{
    public static class StringExtensions
    {
        private static readonly Regex _keyRegex = new Regex("{([^{}:]+)(?::([^{}]+))?}", RegexOptions.Compiled);

        /// <summary>
        /// Named value replacement for strings (modified for ignoring case matching).
        /// Pulled from FluentValidation.
        /// https://github.com/JeremySkinner/FluentValidation/blob/master/src/FluentValidation/Internal/MessageFormatter.cs
        /// </summary>
        /// <param name="template">The template string to format</param>
        /// <param name="values">The key-value based parameters to use for replacment</param>
        /// <param name="ignoreCase">Whether to ignore case matching for the values</param>
        /// <returns></returns>
        public static string Replace(this string template, IDictionary<string, object> values, bool ignoreCase = true)
        {
            var formatValues = ignoreCase ? new Dictionary<string, object>(values, StringComparer.InvariantCultureIgnoreCase) : values;

            return _keyRegex.Replace(template, m =>
            {
                var key = m.Groups[1].Value;

                if (!formatValues.ContainsKey(key))
                    return m.Value;

                var format = m.Groups[2].Success
                    ? $"{{0:{m.Groups[2].Value}}}"
                    : null;

                return format == null
                    ? formatValues[key]?.ToString()
                    : string.Format(CultureInfo.InvariantCulture, format, formatValues[key]);
            });
        }
    }
}