feat: add Russian localization and independent STT languages

src/server/chat-handler.ts

@@ -1,3 +1,5 @@
+import { learningLanguageInstruction } from "../core/i18n.ts";
+import { applicationLanguage, chatLanguage } from "./language.ts";
 import type { Usage } from "@earendil-works/pi-ai";
 import {
 	createPracticeAgent,
@@ -80,6 +82,7 @@ import type {CallUsage, SteerMessage} from "../core/contracts.ts";
  */
 
 const jobRunner = createJobRunner({
+	languageForChat: chatLanguage,
 	chatStore: stores.chatStore,
 	jobStore: stores.jobStore,
 	deliver: deliverJobResult,
@@ -105,6 +108,7 @@ const jobRunner = createJobRunner({
  *  quiz-triggered session runs (turn-service) and notes imports
  *  (/api/graph/import) hit the same single-flight registry. */
 export const extraction = createExtractionPipeline({
+	languageForSource: (id) => chatLanguage(id),
 	...stores,
 	// BYOK (owner, 2026-09-22): the extraction stages resolve the chain —
 	// role override → slot → NOTHING — read FRESH per stage call; an empty
@@ -164,7 +168,7 @@ export async function handleChatRequest(
 		}
 		throw err;
 	}
-	return handleChatInput(chatId, input, buildAgent);
+	return handleChatInput(chatId, input, buildAgent, req.headers.get("accept-language"));
 }
 
 /**
@@ -176,6 +180,7 @@ export async function handleChatInput(
 	chatId: string,
 	input: TurnInput,
 	buildAgent?: (opts: AgentBuildOptions & { teaching: boolean }) => TeachingAgent,
+	browserLanguages?: string | null,
 ): Promise<Response> {
 	let record = stores.chatStore.getChat(chatId);
 	if (!record) {
@@ -191,6 +196,7 @@ export async function handleChatInput(
 	// write-ahead persist (nothing durable changes), and every downstream
 	// resolution (jobs/extraction gate per-need on their own tiers).
 	const effective = effectiveSettings();
+	const language = applicationLanguage(browserLanguages ?? record.language);
 	const conversation = resolveConversationSpec(record.settings, effective.models.strong);
 	if (!conversation) {
 		const envelope = modelsNotConfigured(["strong"]);
@@ -250,7 +256,7 @@ export async function handleChatInput(
 				effective.compaction?.thresholdTokens,
 				catalogContextLimits().get(modelIdForCompaction),
 			),
-			systemPromptTokens: Math.ceil(composeInstructions(record.kind === "practice" ? "practice" : "teacher").length / 4),
+			systemPromptTokens: Math.ceil((composeInstructions(record.kind === "practice" ? "practice" : "teacher").length + learningLanguageInstruction(language).length) / 4),
 		},
 		chatId,
 	);
@@ -312,6 +318,7 @@ export async function handleChatInput(
 	const stagedAutomatic = isSubscriptionProvider(conversation.provider) && input.type === "steers";
 	let persistBaseCount = stagedAutomatic ? record.messages.length : merged.length;
 	try {
+		stores.chatStore.saveLanguage?.(chatId, language);
 		if (!stagedAutomatic) stores.chatStore.saveMessages(chatId, merged);
 		// Dock fix (owner ruling 2026-09-26): persisted markers are visible
 		// in the record — flip their jobs now (the wake's steers ride this
@@ -374,6 +381,7 @@ export async function handleChatInput(
 		restoreAutomatic: (automaticIds, retainedIds) => restoreUncommittedAutomatic(chatId, constructed, automaticIds, retainedIds),
 	});
 	const agentOpts: AgentBuildOptions = {
+		language,
 		engine,
 		callPurpose,
 		requestCycle,
@@ -579,7 +587,7 @@ export async function handleChatInput(
 								fresh.compaction?.thresholdTokens,
 								catalogContextLimits().get(kickModelId),
 							),
-							systemPromptTokens: Math.ceil(composeInstructions(freshRecord.kind === "practice" ? "practice" : "teacher").length / 4),
+							systemPromptTokens: Math.ceil((composeInstructions(freshRecord.kind === "practice" ? "practice" : "teacher").length + learningLanguageInstruction(chatLanguage(chatId)).length) / 4),
 						};
 					}, chatId);
 			},

src/server/index.ts

@@ -44,3 +44,5 @@ export { runPiTurn, piTurnResponse, type PiTurnHandle, type PiTurnSpec } from ".
 export * from "./observability.ts";
 export * from "./model-catalog.ts";
 export { sessionCost } from "./pricing.ts";
+
+export { applicationLanguage, chatLanguage } from "./language.ts";

src/server/language.ts

@@ -0,0 +1,9 @@
+import { resolveLanguage, type Language } from "../core/i18n.ts";
+import { stores } from "./stores.ts";
+/** Explicit app preference wins; automatic follow-ups retain the foreground browser's language. */
+export function applicationLanguage(system?: string | null): Language {
+	return resolveLanguage(stores.settingsStore.readSettings()?.general?.language, system ?? process.env.LH_SYSTEM_LANGUAGE ?? Intl.DateTimeFormat().resolvedOptions().locale);
+}
+export function chatLanguage(chatId: string): Language {
+	return applicationLanguage(stores.chatStore.getChat(chatId)?.language);
+}

src/server/settings-body.ts

@@ -86,6 +86,12 @@ export function parseGeneralSettingsBody(body: unknown): SettingsBodyResult<Gene
 		}
 		settings.autoUpdate = raw.autoUpdate;
 	}
+	for (const key of ["language", "sttLanguage"] as const) {
+		if (raw[key] !== undefined) {
+			if (raw[key] !== "en" && raw[key] !== "ru") return { ok: false, error: `${key} must be "en" or "ru"` };
+			settings[key] = raw[key];
+		}
+	}
 	return { ok: true, settings };
 }