After creating a translation for a localized page using the API the translation is properly created, the page can be opened for edit in the backend and can be previewed. However, when trying to access the live url of the page on the frontend a 404 error is thrown.

The page translation is not published properly.

Use the sample code below to add a translation using Synced localization strategy:

using System;
using System.Globalization;
using System.Linq;
using System.Text.RegularExpressions;
using Telerik.Sitefinity.Localization;
using Telerik.Sitefinity.Modules.Pages;
using Telerik.Sitefinity.Pages.Model;

namespace SitefinityWebApp
{
    public partial class CopyPageDataToAnotherLanguage : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            string sourcePageTitle = "Translate test";
            string titleOfNewTranslatedPage = "Translate test SV";
            string targetCulture = "sv";

            TranslateSyncedPage(sourcePageTitle, targetCulture, titleOfNewTranslatedPage);
        }

        public static void TranslateSyncedPage(string titleOfMainPage, string targetCulture, string titleOftranslatedPage)
        {
            // Get the PageNode
            PageManager manager = PageManager.GetManager();
            PageNode pageNode = manager.GetPageNodes().FirstOrDefault(x => x.Title == titleOfMainPage);

            if (pageNode == null)
            {
                return; // PageNode not found
            }

            CultureInfo targetCultureInfo = CultureInfo.GetCultureInfo(targetCulture);

            // Set values for PageNode properties
            pageNode.Title.SetString(targetCultureInfo, titleOftranslatedPage);
            pageNode.Description.SetString(targetCultureInfo, titleOftranslatedPage);
            pageNode.UrlName.SetString(targetCultureInfo, Regex.Replace(titleOftranslatedPage.ToLower(), @"[^\w\-\!\$\'\(\)\=\@\d_]+", "-"));

            if (pageNode.LocalizationStrategy != LocalizationStrategy.Synced)
            {
                // Set the pageNode LocalizationStrategy for the first method call
                manager.InitializePageLocalizationStrategy(pageNode, LocalizationStrategy.Synced, false);
            }

            PageData pageData = pageNode.GetPageData();

            // Set values for PageData properties 
            pageData.HtmlTitle.SetString(targetCultureInfo, titleOftranslatedPage);
            pageData.Description.SetString(targetCultureInfo, titleOftranslatedPage);
            pageData.Keywords.SetString(targetCultureInfo, titleOftranslatedPage);

            // Publish the page
            pageNode.ApprovalWorkflowState.SetString(targetCultureInfo, "Published");
            manager.SaveChanges();

            var pageDataId = manager.GetPageNode(pageNode.Id).PageId;
            var page = manager.EditPage(pageDataId, targetCultureInfo);

            //publishes draft page
            manager.PublishPageDraft(page, targetCultureInfo);
            manager.SaveChanges();
        }
    }
}

 

For more details about adding a translation to a localized page using both Synced and Split localizations strategies see Sitefinity Documentation, Add a translation to a localized page http://docs.sitefinity.com/for-developers-add-a-translation-to-a-localized-page

Make sure to publish the page translation as shown in the lines marked in yellow in the aboev sample.

References to Other Documentation:
Sitefinity documentation, Add a translation to a localized page https://docs.sitefinity.com/for-developers-add-a-translation-to-a-localized-page