diff --git a/receiverUI/EnvelopeGenerator.ReceiverUI.Web/EnvelopeGenerator.ReceiverUI.Web.Client/Services/LocalizationService.cs b/receiverUI/EnvelopeGenerator.ReceiverUI.Web/EnvelopeGenerator.ReceiverUI.Web.Client/Services/LocalizationService.cs
new file mode 100644
index 00000000..58a7fed7
--- /dev/null
+++ b/receiverUI/EnvelopeGenerator.ReceiverUI.Web/EnvelopeGenerator.ReceiverUI.Web.Client/Services/LocalizationService.cs
@@ -0,0 +1,119 @@
+using EnvelopeGenerator.ReceiverUI.Web.Client.Api;
+
+namespace EnvelopeGenerator.ReceiverUI.Web.Client.Services;
+
+/// <summary>
+/// Pulls all localized strings from the API once and exposes them
+/// via an indexer mimicking <c>IStringLocalizer&lt;Resource&gt;["Key"]</c>
+/// in the legacy MVC Web project.
+///
+/// Missing keys fall back to the key itself (matching the previous behavior
+/// where <c>_localizer["X"].Value</c> returned "X" if not found).
+///
+/// Components consume this service as a scoped dependency and may call
+/// <see cref="EnsureLoadedAsync"/> in <c>OnInitializedAsync</c>.
+/// </summary>
+public class LocalizationService
+{
+    private readonly ReceiverApiClient _api;
+    private readonly ILogger<LocalizationService> _logger;
+    private Dictionary<string, string> _strings = new();
+    private Task? _loadTask;
+    private readonly object _gate = new();
+
+    public LocalizationService(ReceiverApiClient api, ILogger<LocalizationService> logger)
+    {
+        _api = api;
+        _logger = logger;
+    }
+
+    /// <summary>
+    /// Languages exposed in the footer's language switcher. Kept as a
+    /// small in-memory list so the receiver UI does not need an extra
+    /// API roundtrip just to populate a dropdown. Mirrors the cultures
+    /// configured server-side (de-DE, en-US, tr-TR).
+    /// </summary>
+    public static readonly IReadOnlyList<(string Code, string Native, string Flag)> SupportedLanguages =
+        new[]
+        {
+            ("de", "Deutsch",  "fi-de"),
+            ("en", "English",  "fi-gb"),
+            ("tr", "Türkçe",   "fi-tr"),
+        };
+
+    /// <summary>Currently active language code (best effort, set after a switch).</summary>
+    public string? CurrentLanguage { get; private set; }
+
+    /// <summary>Fires whenever the language changes and strings are reloaded.</summary>
+    public event Action? Changed;
+
+    /// <summary>
+    /// Get a localized string by key. Returns the key itself if not found
+    /// (compatible with the legacy <c>_localizer["..."].Value</c> behavior).
+    /// </summary>
+    public string this[string key]
+    {
+        get => _strings.TryGetValue(key, out var v) ? v : key;
+    }
+
+    /// <summary>
+    /// Format a localized template with positional arguments (e.g. "{0}", "{1}").
+    /// </summary>
+    public string Format(string key, params object?[] args)
+    {
+        var template = this[key];
+        try
+        {
+            return string.Format(template, args);
+        }
+        catch (FormatException)
+        {
+            return template;
+        }
+    }
+
+    public IReadOnlyDictionary<string, string> All => _strings;
+
+    /// <summary>
+    /// Loads localization strings from the API. Safe to call multiple times;
+    /// concurrent callers share the same in-flight request.
+    /// </summary>
+    public Task EnsureLoadedAsync(CancellationToken ct = default)
+    {
+        lock (_gate)
+        {
+            return _loadTask ??= LoadCoreAsync(ct);
+        }
+    }
+
+    /// <summary>Forces a reload (e.g. after a language change).</summary>
+    public Task ReloadAsync(CancellationToken ct = default)
+    {
+        lock (_gate)
+        {
+            _loadTask = LoadCoreAsync(ct);
+            return _loadTask;
+        }
+    }
+
+    private async Task LoadCoreAsync(CancellationToken ct)
+    {
+        // Refresh the current language alongside the strings so the
+        // footer dropdown reflects the cookie value picked up by the API.
+        var langTask = _api.GetLanguageAsync(ct);
+        var dict = await _api.GetLocalizationStringsAsync(ct);
+        if (dict is not null)
+            _strings = new Dictionary<string, string>(dict, StringComparer.OrdinalIgnoreCase);
+        else
+            _logger.LogWarning("Localization strings could not be loaded; falling back to keys.");
+        CurrentLanguage = await langTask ?? CurrentLanguage;
+        Changed?.Invoke();
+    }
+
+    public async Task ChangeLanguageAsync(string language, CancellationToken ct = default)
+    {
+        await _api.SetLanguageAsync(language, ct);
+        CurrentLanguage = language;
+        await ReloadAsync(ct);
+    }
+}