feat(install): write launcher language marker files

Some games include a language.txt marker in the unpacked local tree, similar
in spirit to account_name.txt. Installs and updates now carry the launcher
language alongside the account name so those game-provided marker files are
rewritten before staged files are promoted into local/.

The Tauri command boundary keeps the UI setting vocabulary as de/en, then maps
it to the file vocabulary expected by games: german or english. Unknown values
continue through the existing DEFAULT_LANGUAGE path, so the marker file falls
back to english just like script launch arguments fall back to en.

The transaction layer deliberately reuses the same first-match traversal helper
for both marker files. The searches stay independent, so games may place
account_name.txt and language.txt in different directories if their archive
layout requires that.

Test Plan:
- just fmt
- just test
- just frontend-test
- just clippy
- deno task build
- git diff --check

Refs: none

crates/lanspread-peer-cli/src/main.rs

@@ -241,6 +241,7 @@ async fn handle_command(
                 file_descriptions: files,
                 install_after_download: *install_after_download,
                 account_name: None,
+                language: None,
             })?;
             Ok(json!({"queued": true, "game_id": game_id, "install": install_after_download}))
         }
@@ -250,6 +251,7 @@ async fn handle_command(
             sender.send(PeerCommand::InstallGame {
                 id: game_id.clone(),
                 account_name: None,
+                language: None,
             })?;
             Ok(json!({"queued": true, "game_id": game_id}))
         }

crates/lanspread-peer/ARCHITECTURE.md

@@ -116,6 +116,9 @@ Downloaded and installed are independent predicates:
 - `installed` is true when `<game_root>/local/` is a directory. The contents of
   `local/` are user-owned and are skipped by manifests, fingerprints, and file
   serving.
+- Install and update transactions unpack into staging, then overwrite the first
+  discovered game-provided `account_name.txt` and `language.txt` files under
+  the staged tree from launcher settings before promoting it to `local/`.
 
 Reserved per-game paths:
 

crates/lanspread-peer/src/handlers.rs

@@ -200,6 +200,7 @@ pub async fn handle_download_game_files_command(
     file_descriptions: Vec<GameFileDescription>,
     install_after_download: bool,
     account_name: Option<String>,
+    language: Option<String>,
 ) {
     log::info!("Got PeerCommand::DownloadGameFiles");
     if !catalog_contains(ctx, &id).await {
@@ -277,7 +278,7 @@ pub async fn handle_download_game_files_command(
                 log::error!("Failed to send DownloadGameFilesFinished event: {e}");
             }
             if install_after_download {
-                spawn_install_operation(ctx, tx_notify_ui, id.clone(), account_name);
+                spawn_install_operation(ctx, tx_notify_ui, id.clone(), account_name, language);
             }
         } else {
             log::error!("No trusted peers available after majority validation for game {id}");
@@ -364,6 +365,7 @@ pub async fn handle_download_game_files_command(
                             download_id,
                             prepared,
                             account_name,
+                            language,
                         )
                         .await;
                     } else {
@@ -422,8 +424,9 @@ pub async fn handle_install_game_command(
     tx_notify_ui: &UnboundedSender<PeerEvent>,
     id: String,
     account_name: Option<String>,
+    language: Option<String>,
 ) {
-    spawn_install_operation(ctx, tx_notify_ui, id, account_name);
+    spawn_install_operation(ctx, tx_notify_ui, id, account_name, language);
 }
 
 /// Handles the `UninstallGame` command.
@@ -471,11 +474,12 @@ fn spawn_install_operation(
     tx_notify_ui: &UnboundedSender<PeerEvent>,
     id: String,
     account_name: Option<String>,
+    language: Option<String>,
 ) {
     let ctx = ctx.clone();
     let tx_notify_ui = tx_notify_ui.clone();
     ctx.task_tracker.clone().spawn(async move {
-        run_install_operation(&ctx, &tx_notify_ui, id, account_name).await;
+        run_install_operation(&ctx, &tx_notify_ui, id, account_name, language).await;
     });
 }
 
@@ -484,6 +488,7 @@ async fn run_install_operation(
     tx_notify_ui: &UnboundedSender<PeerEvent>,
     id: String,
     account_name: Option<String>,
+    language: Option<String>,
 ) {
     let Some(prepared) = prepare_install_operation(ctx, tx_notify_ui, &id).await else {
         return;
@@ -494,7 +499,7 @@ async fn run_install_operation(
         return;
     }
 
-    run_started_install_operation(ctx, tx_notify_ui, id, prepared, account_name).await;
+    run_started_install_operation(ctx, tx_notify_ui, id, prepared, account_name, language).await;
 }
 
 struct PreparedInstallOperation {
@@ -547,6 +552,7 @@ async fn run_started_install_operation(
     id: String,
     prepared: PreparedInstallOperation,
     account_name: Option<String>,
+    language: Option<String>,
 ) {
     let PreparedInstallOperation {
         game_root,
@@ -577,6 +583,7 @@ async fn run_started_install_operation(
                     &id,
                     ctx.unpacker.clone(),
                     account_name.as_deref(),
+                    language.as_deref(),
                 )
                 .await
             }
@@ -587,6 +594,7 @@ async fn run_started_install_operation(
                     &id,
                     ctx.unpacker.clone(),
                     account_name.as_deref(),
+                    language.as_deref(),
                 )
                 .await
             }
@@ -1503,7 +1511,7 @@ mod tests {
         update_and_announce_games(&ctx, &tx, scan).await;
         assert_local_update(recv_event(&mut rx).await, true, true);
 
-        run_install_operation(&ctx, &tx, "game".to_string(), None).await;
+        run_install_operation(&ctx, &tx, "game".to_string(), None, None).await;
 
         assert_active_update(
             recv_event(&mut rx).await,
@@ -1534,7 +1542,7 @@ mod tests {
         let ctx = test_ctx(temp.path().to_path_buf());
         let (tx, mut rx) = mpsc::unbounded_channel();
 
-        run_install_operation(&ctx, &tx, "game".to_string(), None).await;
+        run_install_operation(&ctx, &tx, "game".to_string(), None, None).await;
 
         assert_active_update(
             recv_event(&mut rx).await,
@@ -1588,7 +1596,8 @@ mod tests {
                         .await
                 );
                 clear_active_download(&ctx, "game").await;
-                run_started_install_operation(&ctx, &tx, "game".to_string(), prepared, None).await;
+                run_started_install_operation(&ctx, &tx, "game".to_string(), prepared, None, None)
+                    .await;
             }
         });
 
@@ -1655,7 +1664,7 @@ mod tests {
         let ctx = test_ctx(temp.path().to_path_buf());
         let (tx, mut rx) = mpsc::unbounded_channel();
 
-        run_install_operation(&ctx, &tx, "game".to_string(), None).await;
+        run_install_operation(&ctx, &tx, "game".to_string(), None, None).await;
 
         assert_active_update(
             recv_event(&mut rx).await,
@@ -1687,7 +1696,7 @@ mod tests {
         let ctx = test_ctx(temp.path().to_path_buf());
         let (tx, mut rx) = mpsc::unbounded_channel();
 
-        run_install_operation(&ctx, &tx, "game".to_string(), None).await;
+        run_install_operation(&ctx, &tx, "game".to_string(), None, None).await;
         assert_active_update(
             recv_event(&mut rx).await,
             active_update("game", ActiveOperationKind::Installing),
@@ -1710,7 +1719,7 @@ mod tests {
         write_file(&root.join("version.ini"), b"20250101");
         write_file(&root.join("game.eti"), b"new archive");
 
-        run_install_operation(&ctx, &tx, "game".to_string(), None).await;
+        run_install_operation(&ctx, &tx, "game".to_string(), None, None).await;
         assert_active_update(
             recv_event(&mut rx).await,
             active_update("game", ActiveOperationKind::Updating),

crates/lanspread-peer/src/install/transaction.rs

@@ -21,6 +21,7 @@ const OWNED_MARKER: &str = ".lanspread_owned";
 const VERSION_TMP_FILE: &str = ".version.ini.tmp";
 const VERSION_DISCARDED_FILE: &str = ".version.ini.discarded";
 const ACCOUNT_NAME_FILE: &str = "account_name.txt";
+const LANGUAGE_FILE: &str = "language.txt";
 
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 enum FsEntryState {
@@ -41,6 +42,7 @@ pub async fn install(
     id: &str,
     unpacker: Arc<dyn Unpacker>,
     account_name: Option<&str>,
+    language: Option<&str>,
 ) -> eyre::Result<()> {
     let eti_version = read_downloaded_version(game_root).await;
     write_intent(
@@ -50,7 +52,7 @@ pub async fn install(
     )
     .await?;
 
-    let result = install_inner(game_root, id, unpacker, account_name).await;
+    let result = install_inner(game_root, id, unpacker, account_name, language).await;
     match result {
         Ok(()) => {
             write_intent(state_dir, id, &InstallIntent::none(id, eti_version)).await?;
@@ -75,6 +77,7 @@ pub async fn update(
     id: &str,
     unpacker: Arc<dyn Unpacker>,
     account_name: Option<&str>,
+    language: Option<&str>,
 ) -> eyre::Result<()> {
     let eti_version = read_downloaded_version(game_root).await;
     write_intent(
@@ -84,7 +87,7 @@ pub async fn update(
     )
     .await?;
 
-    let result = update_inner(game_root, id, unpacker, account_name).await;
+    let result = update_inner(game_root, id, unpacker, account_name, language).await;
     match result {
         Ok(()) => {
             write_intent(state_dir, id, &InstallIntent::none(id, eti_version)).await?;
@@ -193,6 +196,7 @@ async fn install_inner(
     id: &str,
     unpacker: Arc<dyn Unpacker>,
     account_name: Option<&str>,
+    language: Option<&str>,
 ) -> eyre::Result<()> {
     let local = local_dir(game_root);
     if path_is_dir(&local).await {
@@ -202,7 +206,8 @@ async fn install_inner(
     let staging = installing_dir(game_root);
     prepare_owned_empty_dir(&staging).await?;
     unpack_archives(game_root, &staging, unpacker).await?;
-    write_account_name_if_present(&staging, account_name).await?;
+    write_install_setting_if_present(&staging, ACCOUNT_NAME_FILE, account_name).await?;
+    write_install_setting_if_present(&staging, LANGUAGE_FILE, language).await?;
     tokio::fs::rename(&staging, &local)
         .await
         .wrap_err_with(|| format!("failed to promote install for {id}"))?;
@@ -214,6 +219,7 @@ async fn update_inner(
     id: &str,
     unpacker: Arc<dyn Unpacker>,
     account_name: Option<&str>,
+    language: Option<&str>,
 ) -> eyre::Result<()> {
     let local = local_dir(game_root);
     let backup = backup_dir(game_root);
@@ -230,7 +236,8 @@ async fn update_inner(
 
     prepare_owned_empty_dir(&staging).await?;
     unpack_archives(game_root, &staging, unpacker).await?;
-    write_account_name_if_present(&staging, account_name).await?;
+    write_install_setting_if_present(&staging, ACCOUNT_NAME_FILE, account_name).await?;
+    write_install_setting_if_present(&staging, LANGUAGE_FILE, language).await?;
     tokio::fs::rename(&staging, &local)
         .await
         .wrap_err_with(|| format!("failed to promote update for {id}"))?;
@@ -284,25 +291,26 @@ async fn root_eti_archives(game_root: &Path) -> eyre::Result<Vec<PathBuf>> {
     Ok(archives)
 }
 
-async fn write_account_name_if_present(
+async fn write_install_setting_if_present(
     install_root: &Path,
-    account_name: Option<&str>,
+    file_name: &str,
+    value: Option<&str>,
 ) -> eyre::Result<()> {
-    let Some(account_name) = account_name else {
+    let Some(value) = value else {
         return Ok(());
     };
 
-    let Some(path) = find_account_name_file(install_root).await? else {
+    let Some(path) = find_install_setting_file(install_root, file_name).await? else {
         return Ok(());
     };
 
-    tokio::fs::write(&path, account_name)
+    tokio::fs::write(&path, value)
         .await
         .wrap_err_with(|| format!("failed to write {}", path.display()))?;
     Ok(())
 }
 
-async fn find_account_name_file(root: &Path) -> eyre::Result<Option<PathBuf>> {
+async fn find_install_setting_file(root: &Path, file_name: &str) -> eyre::Result<Option<PathBuf>> {
     let mut pending_dirs = vec![root.to_path_buf()];
     while let Some(dir) = pending_dirs.pop() {
         let mut entries = tokio::fs::read_dir(&dir).await?;
@@ -310,7 +318,7 @@ async fn find_account_name_file(root: &Path) -> eyre::Result<Option<PathBuf>> {
         while let Some(entry) = entries.next_entry().await? {
             let file_type = entry.file_type().await?;
             let path = entry.path();
-            if entry.file_name() == OsStr::new(ACCOUNT_NAME_FILE) && file_type.is_file() {
+            if entry.file_name() == OsStr::new(file_name) && file_type.is_file() {
                 return Ok(Some(path));
             }
             if file_type.is_dir() {
@@ -630,7 +638,14 @@ mod tests {
         write_file(&root.join("game.eti"), b"archive");
         write_file(&root.join("version.ini"), b"20250101");
 
-        install(&root, state.path(), "game", successful_unpacker(), None)
+        install(
+            &root,
+            state.path(),
+            "game",
+            successful_unpacker(),
+            None,
+            None,
+        )
         .await
         .expect("install should succeed");
 
@@ -654,6 +669,7 @@ mod tests {
             "game",
             successful_unpacker(),
             Some("Alice"),
+            None,
         )
         .await
         .expect("install should succeed without account file");
@@ -672,7 +688,7 @@ mod tests {
         write_file(&root.join("version.ini"), b"20250101");
         let unpacker = Arc::new(FakeUnpacker::default());
 
-        install(&root, state.path(), "game", unpacker.clone(), None)
+        install(&root, state.path(), "game", unpacker.clone(), None, None)
             .await
             .expect("install should succeed");
 
@@ -687,16 +703,18 @@ mod tests {
     }
 
     #[tokio::test]
-    async fn install_overwrites_first_account_name_file() {
+    async fn install_overwrites_first_install_setting_files() {
-        struct AccountNameUnpacker;
+        struct InstallSettingsUnpacker;
 
-        impl Unpacker for AccountNameUnpacker {
+        impl Unpacker for InstallSettingsUnpacker {
             fn unpack<'a>(&'a self, _archive: &'a Path, dest: &'a Path) -> UnpackFuture<'a> {
                 Box::pin(async move {
                     tokio::fs::create_dir_all(dest.join("a")).await?;
                     tokio::fs::create_dir_all(dest.join("z")).await?;
                     tokio::fs::write(dest.join("a").join(ACCOUNT_NAME_FILE), b"old-a").await?;
                     tokio::fs::write(dest.join("z").join(ACCOUNT_NAME_FILE), b"old-z").await?;
+                    tokio::fs::write(dest.join("a").join(LANGUAGE_FILE), b"old-a").await?;
+                    tokio::fs::write(dest.join("z").join(LANGUAGE_FILE), b"old-z").await?;
                     Ok(())
                 })
             }
@@ -712,8 +730,9 @@ mod tests {
             &root,
             state.path(),
             "game",
-            Arc::new(AccountNameUnpacker),
+            Arc::new(InstallSettingsUnpacker),
             Some("Alice"),
+            Some("german"),
         )
         .await
         .expect("install should succeed");
@@ -728,6 +747,16 @@ mod tests {
                 .expect("second account file should be readable"),
             "old-z"
         );
+        assert_eq!(
+            std::fs::read_to_string(root.join("local").join("a").join(LANGUAGE_FILE))
+                .expect("first language file should be readable"),
+            "german"
+        );
+        assert_eq!(
+            std::fs::read_to_string(root.join("local").join("z").join(LANGUAGE_FILE))
+                .expect("second language file should be readable"),
+            "old-z"
+        );
     }
 
     #[tokio::test]
@@ -745,6 +774,7 @@ mod tests {
             "game",
             Arc::new(FakeUnpacker::failing()),
             None,
+            None,
         )
         .await
         .expect_err("update should fail");
@@ -772,6 +802,7 @@ mod tests {
             "game",
             Arc::new(FakeUnpacker::commit_conflict()),
             None,
+            None,
         )
         .await
         .expect_err("update should fail at commit rename");
@@ -801,7 +832,14 @@ mod tests {
         write_file(&root.join("version.ini"), b"20250101");
         write_file(&root.join("local").join("old.txt"), b"old");
 
-        update(&root, state.path(), "game", successful_unpacker(), None)
+        update(
+            &root,
+            state.path(),
+            "game",
+            successful_unpacker(),
+            None,
+            None,
+        )
         .await
         .expect("update should succeed");
 

crates/lanspread-peer/src/lib.rs

@@ -230,6 +230,7 @@ pub enum PeerCommand {
         id: String,
         file_descriptions: Vec<GameFileDescription>,
         account_name: Option<String>,
+        language: Option<String>,
     },
     /// Download game files with an explicit install policy.
     DownloadGameFilesWithOptions {
@@ -237,11 +238,13 @@ pub enum PeerCommand {
         file_descriptions: Vec<GameFileDescription>,
         install_after_download: bool,
         account_name: Option<String>,
+        language: Option<String>,
     },
     /// Install already-downloaded archives into `local/`.
     InstallGame {
         id: String,
         account_name: Option<String>,
+        language: Option<String>,
     },
     /// Remove only the `local/` install for a game.
     UninstallGame { id: String },
@@ -411,6 +414,7 @@ async fn handle_peer_commands(
                 id,
                 file_descriptions,
                 account_name,
+                language,
             } => {
                 handle_download_game_files_command(
                     ctx,
@@ -419,6 +423,7 @@ async fn handle_peer_commands(
                     file_descriptions,
                     true,
                     account_name,
+                    language,
                 )
                 .await;
             }
@@ -427,6 +432,7 @@ async fn handle_peer_commands(
                 file_descriptions,
                 install_after_download,
                 account_name,
+                language,
             } => {
                 handle_download_game_files_command(
                     ctx,
@@ -435,11 +441,16 @@ async fn handle_peer_commands(
                     file_descriptions,
                     install_after_download,
                     account_name,
+                    language,
                 )
                 .await;
             }
-            PeerCommand::InstallGame { id, account_name } => {
+            PeerCommand::InstallGame {
-                handle_install_game_command(ctx, tx_notify_ui, id, account_name).await;
+                id,
+                account_name,
+                language,
+            } => {
+                handle_install_game_command(ctx, tx_notify_ui, id, account_name, language).await;
             }
             PeerCommand::UninstallGame { id } => {
                 handle_uninstall_game_command(ctx, tx_notify_ui, id).await;

crates/lanspread-tauri-deno-ts/src-tauri/src/lib.rs

@@ -42,10 +42,16 @@ struct LanSpreadState {
     peer_game_db: Arc<RwLock<PeerGameDB>>,
     catalog: Arc<RwLock<HashSet<String>>>,
     unpack_logs: Arc<RwLock<Vec<UnpackLogEntry>>>,
-    pending_install_account_names: Arc<RwLock<HashMap<String, String>>>,
+    pending_install_settings: Arc<RwLock<HashMap<String, InstallSettings>>>,
     state_dir: OnceLock<PathBuf>,
 }
 
+#[derive(Clone, Debug, PartialEq, Eq)]
+struct InstallSettings {
+    account_name: String,
+    language: String,
+}
+
 struct PeerEventTx(UnboundedSender<PeerEvent>);
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq, serde::Serialize)]
@@ -145,6 +151,7 @@ async fn request_games(state: tauri::State<'_, LanSpreadState>) -> tauri::Result
 #[tauri::command]
 async fn install_game(
     id: String,
+    language: String,
     username: String,
     state: tauri::State<'_, LanSpreadState>,
 ) -> tauri::Result<bool> {
@@ -173,20 +180,21 @@ async fn install_game(
         return Ok(false);
     };
 
-    let account_name = sanitize_username(&username);
+    let install_settings = install_settings(&language, &username);
     let handled = if let Some(peer_ctrl) = peer_ctrl {
         let command = if !downloaded {
             state
                 .inner()
-                .pending_install_account_names
+                .pending_install_settings
                 .write()
                 .await
-                .insert(id.clone(), account_name);
+                .insert(id.clone(), install_settings);
             PeerCommand::GetGame(id.clone())
         } else if !installed {
             PeerCommand::InstallGame {
                 id: id.clone(),
-                account_name: Some(account_name),
+                account_name: Some(install_settings.account_name),
+                language: Some(install_settings.language),
             }
         } else {
             log::info!("Game is already installed: {id}");
@@ -197,7 +205,7 @@ async fn install_game(
             log::error!("Failed to send message to peer: {e:?}");
             state
                 .inner()
-                .pending_install_account_names
+                .pending_install_settings
                 .write()
                 .await
                 .remove(&id);
@@ -215,6 +223,7 @@ async fn install_game(
 #[tauri::command]
 async fn update_game(
     id: String,
+    language: String,
     username: String,
     state: tauri::State<'_, LanSpreadState>,
 ) -> tauri::Result<bool> {
@@ -236,15 +245,15 @@ async fn update_game(
     if let Some(peer_ctrl) = peer_ctrl {
         state
             .inner()
-            .pending_install_account_names
+            .pending_install_settings
             .write()
             .await
-            .insert(id.clone(), sanitize_username(&username));
+            .insert(id.clone(), install_settings(&language, &username));
         if let Err(e) = peer_ctrl.send(PeerCommand::FetchLatestFromPeers { id: id.clone() }) {
             log::error!("Failed to send message to peer: {e:?}");
             state
                 .inner()
-                .pending_install_account_names
+                .pending_install_settings
                 .write()
                 .await
                 .remove(&id);
@@ -342,7 +351,7 @@ async fn cancel_download(
 ) -> tauri::Result<bool> {
     state
         .inner()
-        .pending_install_account_names
+        .pending_install_settings
         .write()
         .await
         .remove(&id);
@@ -459,6 +468,20 @@ fn launch_settings(language: &str, username: &str) -> LaunchSettings {
     }
 }
 
+fn install_settings(language: &str, username: &str) -> InstallSettings {
+    InstallSettings {
+        account_name: sanitize_username(username),
+        language: install_language(language),
+    }
+}
+
+fn install_language(language: &str) -> String {
+    match sanitize_language(language).as_str() {
+        "de" => "german".to_string(),
+        _ => "english".to_string(),
+    }
+}
+
 #[cfg_attr(not(target_os = "windows"), allow(dead_code))]
 fn sanitize_language(language: &str) -> String {
     match language.trim().to_ascii_lowercase().as_str() {
@@ -1481,7 +1504,7 @@ async fn handle_peer_event(app_handle: &AppHandle, event: PeerEvent) {
         }
         PeerEvent::NoPeersHaveGame { id } => {
             log::warn!("PeerEvent::NoPeersHaveGame received for {id}");
-            clear_pending_install_account_name(app_handle, &id).await;
+            clear_pending_install_settings(app_handle, &id).await;
             emit_game_id_event(
                 app_handle,
                 "game-no-peers",
@@ -1520,7 +1543,7 @@ async fn handle_peer_event(app_handle: &AppHandle, event: PeerEvent) {
         }
         PeerEvent::DownloadGameFilesFailed { id } => {
             log::warn!("PeerEvent::DownloadGameFilesFailed received");
-            clear_pending_install_account_name(app_handle, &id).await;
+            clear_pending_install_settings(app_handle, &id).await;
             emit_game_id_event(
                 app_handle,
                 "game-download-failed",
@@ -1530,7 +1553,7 @@ async fn handle_peer_event(app_handle: &AppHandle, event: PeerEvent) {
         }
         PeerEvent::DownloadGameFilesAllPeersGone { id } => {
             log::warn!("PeerEvent::DownloadGameFilesAllPeersGone received for {id}");
-            clear_pending_install_account_name(app_handle, &id).await;
+            clear_pending_install_settings(app_handle, &id).await;
             emit_game_id_event(
                 app_handle,
                 "game-download-peers-gone",
@@ -1655,9 +1678,9 @@ async fn handle_peer_event(app_handle: &AppHandle, event: PeerEvent) {
     }
 }
 
-async fn clear_pending_install_account_name(app_handle: &AppHandle, id: &str) {
+async fn clear_pending_install_settings(app_handle: &AppHandle, id: &str) {
     let state = app_handle.state::<LanSpreadState>();
-    state.pending_install_account_names.write().await.remove(id);
+    state.pending_install_settings.write().await.remove(id);
 }
 
 async fn handle_got_game_files(
@@ -1674,17 +1697,17 @@ async fn handle_got_game_files(
     );
 
     let state = app_handle.state::<LanSpreadState>();
-    let account_name = state
+    let install_settings = state.pending_install_settings.write().await.remove(&id);
-        .pending_install_account_names
+    let (account_name, language) = install_settings.map_or((None, None), |settings| {
-        .write()
+        (Some(settings.account_name), Some(settings.language))
-        .await
+    });
-        .remove(&id);
     let peer_ctrl = state.peer_ctrl.read().await.clone();
     if let Some(peer_ctrl) = peer_ctrl
         && let Err(e) = peer_ctrl.send(PeerCommand::DownloadGameFiles {
             id,
             file_descriptions,
             account_name,
+            language,
         })
     {
         log::error!("Failed to send PeerCommand::DownloadGameFiles: {e}");
@@ -1921,6 +1944,24 @@ mod tests {
         );
     }
 
+    #[test]
+    fn install_settings_use_language_file_values() {
+        assert_eq!(
+            install_settings("de", "  Alice \"Ace\"%PATH%\n  "),
+            InstallSettings {
+                account_name: "Alice AcePATH".to_string(),
+                language: "german".to_string(),
+            }
+        );
+        assert_eq!(
+            install_settings("fr", ""),
+            InstallSettings {
+                account_name: DEFAULT_USERNAME.to_string(),
+                language: "english".to_string(),
+            }
+        );
+    }
+
     #[test]
     fn script_params_use_common_argument_shape() {
         let start_params = script_params(

crates/lanspread-tauri-deno-ts/src/hooks/useGameActions.ts

@@ -53,6 +53,7 @@ export const useGameActions = (
         try {
             const success = await invoke<boolean>('install_game', {
                 id,
+                language: settings.language,
                 username: settings.username,
             });
             if (!success) return;
@@ -64,19 +65,20 @@ export const useGameActions = (
         } catch (err) {
             console.error('install_game failed:', err);
         }
-    }, [games, settings.username]);
+    }, [games, settings.language, settings.username]);
 
     const update = useCallback(async (id: string) => {
         try {
             const success = await invoke<boolean>('update_game', {
                 id,
+                language: settings.language,
                 username: settings.username,
             });
             if (success) games.markChecking(id);
         } catch (err) {
             console.error('update_game failed:', err);
         }
-    }, [games, settings.username]);
+    }, [games, settings.language, settings.username]);
 
     const uninstall = useCallback(async (id: string) => {
         try {