The composer says which language a post is in

A post went out in the reader's own interface language whatever it was
written in. The composer now has a language picker (each language named in
itself), starting at the persona's default from Settings, else the
interface's; a reply starts in its thread's language. The e2e poll test
picks Italian and finds it on PrivaPub.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

Components/Composer.razor

@@ -129,6 +129,17 @@
 				</DDropdown>
 			}
 
+			@if (!form.IsLocated && GroupId is null && Editing is null)
+			{
+				@* the language the post is written in, as each language names itself *@
+				<DSelect TValue="string" Size="DSize.Sm" class="w-auto" @bind-Value="form.Language" title="@Localizer["Language"]" data-compose-language>
+					@foreach (var (languageCode, languageName) in Languages.All)
+					{
+						<option value="@languageCode">@languageName</option>
+					}
+				</DSelect>
+			}
+
 			<DButton Size="DSize.Sm" Active="form.HasContentWarning" OnClick="() => form.HasContentWarning = !form.HasContentWarning" title="@Localizer["Content warning"]">
 				<i class="ion-md-warning text-base"></i>
 			</DButton>
@@ -258,6 +269,10 @@
 		_ => default
 	};
 
+	// a new post starts in the language the persona chose in Settings, else in the reader's
+	string DefaultLanguage => CascadingState.Persona?.Source?.Language is { Length: > 0 } chosen ? chosen
+		: System.Globalization.CultureInfo.CurrentUICulture.TwoLetterISOLanguageName;
+
 	// a new post starts with the visibility the persona chose in Settings
 	MessageType DefaultVisibility => CascadingState.Persona?.Source?.Privacy switch
 	{
@@ -270,6 +285,7 @@
 	{
 		form.GroupId = GroupId;
 		form.MessageType = DefaultVisibility;
+		form.Language = DefaultLanguage;
 		form.QuotedStatusId = Quoting?.Id;
 		if (Editing is not null)
 		{
@@ -290,6 +306,8 @@
 			"unlisted" => MessageType.Unlisted,
 			_ => MessageType.Public
 		};
+		// a reply is written in its thread's language, as a rule
+		form.Language = InReplyTo.Language is { Length: 2 } language && Languages.All.Any(l => l.Code == language) ? language : form.Language;
 		form.HasContentWarning = InReplyTo.SpoilerText is { Length: > 0 };
 		form.SpoilerText = InReplyTo.SpoilerText;
 		var mentions = InReplyTo.Mentions.Select(m => m.Acct).Prepend(InReplyTo.Account?.Acct)
@@ -430,14 +448,14 @@
 		if (result.Data is ScheduledStatus scheduled)
 		{
 			Toast.AddResponseSuccess(Localizer["Scheduled for {0}.", scheduled.ScheduledAt.ToLocalTime().ToString(SUtility.dateTimeFormatExt)]);
-			form = new() { GroupId = GroupId, MessageType = DefaultVisibility };
+			form = new() { GroupId = GroupId, MessageType = DefaultVisibility, Language = DefaultLanguage };
 			await OnPublished.InvokeAsync(null);
 			return;
 		}
 
 		Toast.AddResponseSuccess(form.IsLocated ? Localizer["Located post published."] : Localizer["Published."]);
 		var published = result.Data as FeedPost;
-		form = new() { GroupId = GroupId, MessageType = DefaultVisibility };
+		form = new() { GroupId = GroupId, MessageType = DefaultVisibility, Language = DefaultLanguage };
 		await OnPublished.InvokeAsync(published);
 	}
 

Models/ComposeForm.cs

@@ -43,6 +43,9 @@ public class ComposeForm
 	public int PollExpiresIn { get; set; } = 86400;
 	public bool PollMultiple { get; set; }
 
+	/// <summary>The language the post is written in (ISO 639-1); null leaves it to PrivaPub.</summary>
+	public string Language { get; set; }
+
 	/// <summary>The post this one quotes.</summary>
 	public string QuotedStatusId { get; set; }
 

Services/StatusService.cs

@@ -54,7 +54,7 @@ namespace decePubClient.Services
 				Sensitive = form.HasContentWarning,
 				SpoilerText = form.HasContentWarning ? form.SpoilerText : null,
 				Visibility = form.Visibility,
-				Language = CultureInfo.CurrentUICulture.TwoLetterISOLanguageName,
+				Language = form.Language ?? CultureInfo.CurrentUICulture.TwoLetterISOLanguageName,
 				ScheduledAt = form.ScheduledAtUtc?.ToString("o", CultureInfo.InvariantCulture),
 				Poll = form.HasPoll ? new PollForm { Options = [.. form.PollOptions.Select(o => o.Trim()).Where(o => o.Length > 0)], ExpiresIn = form.PollExpiresIn, Multiple = form.PollMultiple } : null,
 				QuotedStatusId = form.QuotedStatusId

tests/e2e/Actions/ComposerTests.cs

@@ -6,7 +6,8 @@ using Microsoft.Playwright;
 
 namespace decePubClient.E2E.Actions
 {
-	// The composer beyond words: a poll, the persona's own post edited, and a quote, each checked on PrivaPub
+	// The composer beyond words: a poll in a language picked, the persona's own post edited, and a quote, each checked on
+	// PrivaPub
 	public sealed class ComposerTests(Browser browser)
 	{
 		static async Task OpenHome(IPage page)
@@ -39,12 +40,15 @@ namespace decePubClient.E2E.Actions
 					var choices = page.Locator("[data-poll-editor] input[type=text]");
 					await choices.Nth(0).FillAsync("tea");
 					await choices.Nth(1).FillAsync("coffee");
+					// and in the language picked
+					await page.Locator("[data-compose-language]").First.SelectOptionAsync("it");
 					await page.GetByRole(AriaRole.Button, new() { Name = "Post" }).Last.ClickAsync();
 					JsonNode latest = null;
 					Assert.True(await Pasture.Eventually(async () => (latest = await Latest(persona))?["content"]?.GetValue<string>().Contains(text) == true, 15),
 						"the poll was never published");
 					made = latest!["id"]!.GetValue<string>();
 					Assert.Equal(new[] { "tea", "coffee" }, latest["poll"]!["options"]!.AsArray().Select(o => o!["title"]!.GetValue<string>()));
+					Assert.Equal("it", latest["language"]?.GetValue<string>());
 					await session.AssertGuards();
 				}, page);
 			}