Optimizely World blog post: Custom placeholders in Optimizely Forms submission emails. https://world.optimizely.com/blogs/Antti-Alasvuo/Dates/2022/6/custom-place-holders-in-optimizely-forms-submission-emails/

FormSubmissionDataExtensions.cs

using System;
using System.Collections.Generic;
using EPiServer.Core;
using EPiServer.Forms;
using EPiServer.Forms.Core.Models;

namespace AlloyWithFind.Features.FormsCustomPlaceholder
{
    /// <summary>
    /// Extension methods for <see cref="Submission.Data"/>.
    /// </summary>
    public static class FormSubmissionDataExtensions
    {
        /// <summary>
        /// Tries to get the language code.
        /// </summary>
        /// <param name="data"><see cref="Submission.Data"/> dictionaty to be extended.</param>
        /// <param name="languageCode">Language code.</param>
        /// <returns>True if the language code was in the data and the value is not null or empty or just whitespace characters, otherwise false.</returns>
        public static bool TryGetLanguage(this IDictionary<string, object> data, out string languageCode)
        {
            languageCode = null;

            // language type is string
            if (data != null && data.TryGetValue(Constants.SYSTEMCOLUMN_Language, out object language) && language is string lang && !string.IsNullOrWhiteSpace(lang))
            {
                languageCode = lang;
                return true;
            }

            return false;
        }

        /// <summary>
        /// Tries to get the submit time.
        /// </summary>
        /// <param name="data"><see cref="Submission.Data"/> dictionaty to be extended.</param>
        /// <param name="submitted">DateTime when the data was submitted.</param>
        /// <returns>True if there was a submit time otherwise false.</returns>
        public static bool TryGetSubmitTime(this IDictionary<string, object> data, out DateTime submitted)
        {
            submitted = DateTime.MinValue;

            // submit time type is DateTime
            if (data != null && data.TryGetValue(Constants.SYSTEMCOLUMN_SubmitTime, out object submitTime) && submitTime is DateTime timestamp)
            {
                submitted = timestamp;
                return true;
            }

            return false;
        }

        /// <summary>
        /// Tries to get the username.
        /// </summary>
        /// <param name="data"><see cref="Submission.Data"/> dictionaty to be extended.</param>
        /// <param name="username">Username for the submitted data (Note! This value can be null).</param>
        /// <returns>True if the data contained the username otherwise false.</returns>
        public static bool TryGetSubmitUser(this IDictionary<string, object> data, out string username)
        {
            username = null;

            // submit user type is string
            if (data != null && data.TryGetValue(Constants.SYSTEMCOLUMN_SubmitUser, out object submitUser) && submitUser is string user)
            {
                username = user;
                return true;
            }

            return false;
        }

        /// <summary>
        /// Tries to get the hosted page ContentReference.
        /// </summary>
        /// <param name="data"><see cref="Submission.Data"/> dictionaty to be extended.</param>
        /// <param name="contentLink">ContentReference to the hosted page.</param>
        /// <returns>True hosted page ContentReference was resolved otherwise false.</returns>
        public static bool TryGetHostedPage(this IDictionary<string, object> data, out ContentReference contentLink)
        {
            contentLink = null;

            // hosted page type is string
            if (data != null && data.TryGetValue(Constants.SYSTEMCOLUMN_HostedPage, out object hp) && hp is string hostedPage
                && ContentReference.TryParse(hostedPage, out contentLink))
            {
                return true;
            }

            return false;
        }
    }
}