C# Deepl API HTTP Response 403

Question

I want to have a tool, that can transalte Words or sentences from a source language into various selctable languages and put it together in a certain string. For this I wanted to use DeepL API. When I'm trying to use the tool, I will get the HTTP response 403-Forbidden.

XAML:

<Window x:Class="DeepL_Translator.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="DeepL Translator" Height="450" Width="800">
    <Grid>
        <StackPanel Margin="10">
            <Label Content="Text zu übersetzen:" />
            <TextBox x:Name="txtInput" TextWrapping="Wrap" Height="100" />
            <Label Content="Zielsprachen:" />
            <StackPanel Orientation="Horizontal">
                <CheckBox x:Name="chkEnglish" Content="Englisch (Britisch)" IsChecked="True" />
                <CheckBox x:Name="chkCzech" Content="Tschechisch" />
                <CheckBox x:Name="chkSpanish" Content="Spanisch" />
                <CheckBox x:Name="chkPortuguese" Content="Portugiesisch (Brasilien)" />
                <CheckBox x:Name="chkFrench" Content="Französisch" />
            </StackPanel>
            <Button x:Name="btnTranslate" Content="Übersetzen" Click="BtnTranslate_Click" />
            <Label Content="Übersetzter Text:" />
            <TextBox x:Name="txtOutput" TextWrapping="Wrap" Height="100" />
        </StackPanel>
    </Grid>
</Window>

C#:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net.Http;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using Newtonsoft.Json.Linq;
using DeepL_Translator.Languages;
using DeepL;

namespace DeepL_Translator
{
    public enum LanguageCode
    {
        EN,
        CS,
        ES,
        PT,
        FR,
        DE,
    }

    public partial class MainWindow : Window
    {
        private const string API_KEY = "f0798faa-..."; // Replace with actual key
        private const string API_URL = "https://api-free.deepl.com/v2/translate";

        public MainWindow()
        {
            InitializeComponent();
        }

        private void BtnTranslate_Click(object sender, RoutedEventArgs e)
        {
            string text = txtInput.Text;
            List<string> targetLanguages = new List<string>();

            // Get selected target languages
            if (chkEnglish.IsChecked.Value) targetLanguages.Add("EN-GB");
            if (chkCzech.IsChecked.Value) targetLanguages.Add("CS");
            if (chkSpanish.IsChecked.Value) targetLanguages.Add("ES");
            if (chkPortuguese.IsChecked.Value) targetLanguages.Add("PT-BR");
            if (chkFrench.IsChecked.Value) targetLanguages.Add("FR");

            // Create the HTTP request
            using (HttpClient client = new HttpClient())
            {
                string targetLangString = "";
                foreach (var langCode in targetLanguages)
                {
                    targetLangString += langCode.ToString().ToUpper() + ",";
                }

                // Remove the trailing comma
                targetLangString = targetLangString.TrimEnd(',');

                string requestUrl = $"{API_URL}?auth_key={API_KEY}&text={text}&source_lang=DE&target_langs={targetLangString}";

                try
                {
                    var response = client.GetAsync(requestUrl).Result;

                    // Parse the JSON response
                    if (response.IsSuccessStatusCode)
                    {
                        string jsonResponse = response.Content.ReadAsStringAsync().Result;
                        JObject json = JObject.Parse(jsonResponse);

                        // Get the translated text
                        StringBuilder sbOutput = new StringBuilder();
                        sbOutput.AppendLine("{i18n de}").AppendLine(text).AppendLine("{/i18n}");
                        foreach (JObject translation in json["translations"])
                        {
                            sbOutput.AppendLine("{i18n " + translation["target_lang"].ToString().ToLower() + "}");
                            sbOutput.AppendLine(translation["text"].ToString());
                            sbOutput.AppendLine("{/i18n}");
                        }

                        txtOutput.Text = sbOutput.ToString();
                    }
                    else
                    {
                        MessageBox.Show($"An error occurred while translating the text. Status code: {response.StatusCode}", "Error", MessageBoxButton.OK, MessageBoxImage.Error);
                    }
                }
                catch (Exception ex)
                {
                    // Handle other potential exceptions (e.g., network issues)
                    MessageBox.Show($"An error occurred: {ex.Message}", "Error", MessageBoxButton.OK, MessageBoxImage.Error);
                }
            }
        }
    }
}

I tracked via Fiddler Everywhere. The Request looks like that:

https://api-free.deepl.com/v2/translate?auth_key=f0798faa-...&text=hallo&source_lang=DE&target_langs=EN-GB

I tried various kinds of DeepL-API-URLs, with the same result.

Answer 1

The current version of the DeepL API (v2) uses POST v2/translate and expects a JSON object in the body providing the text and target_lang parameters at minimum.

Your Auth Key should be provided in the Authorization header of your request.

POST /v2/translate HTTP/2
Host: api-free.deepl.com
Authorization: DeepL-Auth-Key [yourAuthKey] 
User-Agent: YourApp/1.2.3
Content-Length: 45
Content-Type: application/json

{"text":["Hello, world!"],"target_lang":"DE"}

I suggest you take a look at the documentation for Translate Text.