feat: add global language instruction setting for AI responses

apps/server/src/index.ts

@@ -219,7 +219,7 @@ app.get('/api/health/detailed', createDetailedHandler());
 app.use('/api/fs', createFsRoutes(events));
 app.use('/api/agent', createAgentRoutes(agentService, events));
 app.use('/api/sessions', createSessionsRoutes(agentService));
-app.use('/api/features', createFeaturesRoutes(featureLoader));
+app.use('/api/features', createFeaturesRoutes(featureLoader, settingsService));
 app.use('/api/auto-mode', createAutoModeRoutes(autoModeService));
 app.use('/api/enhance-prompt', createEnhancePromptRoutes(settingsService));
 app.use('/api/worktree', createWorktreeRoutes(events, settingsService));

apps/server/src/lib/settings-helpers.ts

@@ -5,12 +5,18 @@
 import type { SettingsService } from '../services/settings-service.js';
 import type { ContextFilesResult, ContextFileInfo } from '@automaker/utils';
 import { createLogger } from '@automaker/utils';
-import type { MCPServerConfig, McpServerConfig, PromptCustomization } from '@automaker/types';
+import type {
+  MCPServerConfig,
+  McpServerConfig,
+  PromptCustomization,
+  LanguageInstruction,
+} from '@automaker/types';
 import {
   mergeAutoModePrompts,
   mergeAgentPrompts,
   mergeBacklogPlanPrompts,
   mergeEnhancementPrompts,
+  prependLanguageInstruction,
 } from '@automaker/prompts';
 
 const logger = createLogger('SettingsHelper');
@@ -205,6 +211,7 @@ function convertToSdkFormat(server: MCPServerConfig): McpServerConfig {
 /**
  * Get prompt customization from global settings and merge with defaults.
  * Returns prompts merged with built-in defaults - custom prompts override defaults.
+ * Also applies language instruction to all system prompts if enabled.
  *
  * @param settingsService - Optional settings service instance
  * @param logPrefix - Prefix for log messages
@@ -218,14 +225,20 @@ export async function getPromptCustomization(
   agent: ReturnType<typeof mergeAgentPrompts>;
   backlogPlan: ReturnType<typeof mergeBacklogPlanPrompts>;
   enhancement: ReturnType<typeof mergeEnhancementPrompts>;
+  languageInstruction?: LanguageInstruction;
 }> {
   let customization: PromptCustomization = {};
+  let languageInstruction: LanguageInstruction | undefined;
 
   if (settingsService) {
     try {
       const globalSettings = await settingsService.getGlobalSettings();
       customization = globalSettings.promptCustomization || {};
+      languageInstruction = globalSettings.languageInstruction;
       logger.info(`${logPrefix} Loaded prompt customization from settings`);
+      if (languageInstruction?.enabled) {
+        logger.info(`${logPrefix} Language instruction enabled: ${languageInstruction.language}`);
+      }
     } catch (error) {
       logger.error(`${logPrefix} Failed to load prompt customization:`, error);
       // Fall through to use empty customization (all defaults)
@@ -234,14 +247,95 @@ export async function getPromptCustomization(
     logger.info(`${logPrefix} SettingsService not available, using default prompts`);
   }
 
+  // Merge prompts with defaults
+  const mergedAutoMode = mergeAutoModePrompts(customization.autoMode);
+  const mergedAgent = mergeAgentPrompts(customization.agent);
+  const mergedBacklogPlan = mergeBacklogPlanPrompts(customization.backlogPlan);
+  const mergedEnhancement = mergeEnhancementPrompts(customization.enhancement);
+
+  // Apply language instruction to system prompts if enabled
   return {
-    autoMode: mergeAutoModePrompts(customization.autoMode),
-    agent: mergeAgentPrompts(customization.agent),
-    backlogPlan: mergeBacklogPlanPrompts(customization.backlogPlan),
-    enhancement: mergeEnhancementPrompts(customization.enhancement),
+    autoMode: {
+      planningLite: prependLanguageInstruction(mergedAutoMode.planningLite, languageInstruction),
+      planningLiteWithApproval: prependLanguageInstruction(
+        mergedAutoMode.planningLiteWithApproval,
+        languageInstruction
+      ),
+      planningSpec: prependLanguageInstruction(mergedAutoMode.planningSpec, languageInstruction),
+      planningFull: prependLanguageInstruction(mergedAutoMode.planningFull, languageInstruction),
+      featurePromptTemplate: prependLanguageInstruction(
+        mergedAutoMode.featurePromptTemplate,
+        languageInstruction
+      ),
+      followUpPromptTemplate: prependLanguageInstruction(
+        mergedAutoMode.followUpPromptTemplate,
+        languageInstruction
+      ),
+      continuationPromptTemplate: prependLanguageInstruction(
+        mergedAutoMode.continuationPromptTemplate,
+        languageInstruction
+      ),
+      pipelineStepPromptTemplate: prependLanguageInstruction(
+        mergedAutoMode.pipelineStepPromptTemplate,
+        languageInstruction
+      ),
+    },
+    agent: {
+      systemPrompt: prependLanguageInstruction(mergedAgent.systemPrompt, languageInstruction),
+    },
+    backlogPlan: {
+      systemPrompt: prependLanguageInstruction(mergedBacklogPlan.systemPrompt, languageInstruction),
+      userPromptTemplate: mergedBacklogPlan.userPromptTemplate,
+    },
+    enhancement: {
+      improveSystemPrompt: prependLanguageInstruction(
+        mergedEnhancement.improveSystemPrompt,
+        languageInstruction
+      ),
+      technicalSystemPrompt: prependLanguageInstruction(
+        mergedEnhancement.technicalSystemPrompt,
+        languageInstruction
+      ),
+      simplifySystemPrompt: prependLanguageInstruction(
+        mergedEnhancement.simplifySystemPrompt,
+        languageInstruction
+      ),
+      acceptanceSystemPrompt: prependLanguageInstruction(
+        mergedEnhancement.acceptanceSystemPrompt,
+        languageInstruction
+      ),
+      uxReviewerSystemPrompt: prependLanguageInstruction(
+        mergedEnhancement.uxReviewerSystemPrompt,
+        languageInstruction
+      ),
+    },
+    languageInstruction,
   };
 }
 
+/**
+ * Get language instruction from global settings.
+ * Use this when you need to apply language instruction separately from prompt customization.
+ *
+ * @param settingsService - Optional settings service instance
+ * @returns Promise resolving to the language instruction or undefined if not set
+ */
+export async function getLanguageInstruction(
+  settingsService?: SettingsService | null
+): Promise<LanguageInstruction | undefined> {
+  if (!settingsService) {
+    return undefined;
+  }
+
+  try {
+    const globalSettings = await settingsService.getGlobalSettings();
+    return globalSettings.languageInstruction;
+  } catch (error) {
+    logger.error('[SettingsHelper] Failed to load language instruction:', error);
+    return undefined;
+  }
+}
+
 /**
  * Get Skills configuration from settings.
  * Returns configuration for enabling skills and which sources to load from.

apps/server/src/routes/app-spec/generate-features-from-spec.ts

@@ -14,7 +14,8 @@ import { streamingQuery } from '../../providers/simple-query-service.js';
 import { parseAndCreateFeatures } from './parse-and-create-features.js';
 import { getAppSpecPath } from '@automaker/platform';
 import type { SettingsService } from '../../services/settings-service.js';
-import { getAutoLoadClaudeMdSetting } from '../../lib/settings-helpers.js';
+import { getAutoLoadClaudeMdSetting, getLanguageInstruction } from '../../lib/settings-helpers.js';
+import { prependLanguageInstruction } from '@automaker/prompts';
 
 const logger = createLogger('SpecRegeneration');
 
@@ -53,7 +54,7 @@ export async function generateFeaturesFromSpec(
     return;
   }
 
-  const prompt = `Based on this project specification:
+  const basePrompt = `Based on this project specification:
 
 ${spec}
 
@@ -86,6 +87,10 @@ Generate ${featureCount} features that build on each other logically.
 
 IMPORTANT: Do not ask for clarification. The specification is provided above. Generate the JSON immediately.`;
 
+  // Load language instruction from settings
+  const languageInstruction = await getLanguageInstruction(settingsService);
+  const prompt = prependLanguageInstruction(basePrompt, languageInstruction);
+
   logger.info('========== PROMPT BEING SENT ==========');
   logger.info(`Prompt length: ${prompt.length} chars`);
   logger.info(`Prompt preview (first 1000 chars):\n${prompt.substring(0, 1000)}`);

apps/server/src/routes/app-spec/generate-spec.ts

@@ -21,7 +21,8 @@ import { streamingQuery } from '../../providers/simple-query-service.js';
 import { generateFeaturesFromSpec } from './generate-features-from-spec.js';
 import { ensureAutomakerDir, getAppSpecPath } from '@automaker/platform';
 import type { SettingsService } from '../../services/settings-service.js';
-import { getAutoLoadClaudeMdSetting } from '../../lib/settings-helpers.js';
+import { getAutoLoadClaudeMdSetting, getLanguageInstruction } from '../../lib/settings-helpers.js';
+import { prependLanguageInstruction } from '@automaker/prompts';
 
 const logger = createLogger('SpecRegeneration');
 
@@ -66,7 +67,7 @@ export async function generateSpec(
 Use these technologies as the foundation for the specification.`;
   }
 
-  const prompt = `You are helping to define a software project specification.
+  const basePrompt = `You are helping to define a software project specification.
 
 IMPORTANT: Never ask for clarification or additional information. Use the information provided and make reasonable assumptions to create the best possible specification. If details are missing, infer them based on common patterns and best practices.
 
@@ -79,6 +80,10 @@ ${analysisInstructions}
 
 ${getStructuredSpecPromptInstruction()}`;
 
+  // Load language instruction from settings
+  const languageInstruction = await getLanguageInstruction(settingsService);
+  const prompt = prependLanguageInstruction(basePrompt, languageInstruction);
+
   logger.info('========== PROMPT BEING SENT ==========');
   logger.info(`Prompt length: ${prompt.length} chars`);
   logger.info(`Prompt preview (first 500 chars):\n${prompt.substring(0, 500)}`);

apps/server/src/routes/context/routes/describe-file.ts

@@ -19,7 +19,11 @@ import { simpleQuery } from '../../../providers/simple-query-service.js';
 import * as secureFs from '../../../lib/secure-fs.js';
 import * as path from 'path';
 import type { SettingsService } from '../../../services/settings-service.js';
-import { getAutoLoadClaudeMdSetting } from '../../../lib/settings-helpers.js';
+import {
+  getAutoLoadClaudeMdSetting,
+  getLanguageInstruction,
+} from '../../../lib/settings-helpers.js';
+import { prependLanguageInstruction } from '@automaker/prompts';
 
 const logger = createLogger('DescribeFile');
 
@@ -132,7 +136,7 @@ export function createDescribeFileHandler(
 
       // Build prompt with file content passed as structured data
       // The file content is included directly, not via tool invocation
-      const prompt = `Analyze the following file and provide a 1-2 sentence description suitable for use as context in an AI coding assistant. Focus on what the file contains, its purpose, and why an AI agent might want to use this context in the future (e.g., "API documentation for the authentication endpoints", "Configuration file for database connections", "Coding style guidelines for the project").
+      const basePrompt = `Analyze the following file and provide a 1-2 sentence description suitable for use as context in an AI coding assistant. Focus on what the file contains, its purpose, and why an AI agent might want to use this context in the future (e.g., "API documentation for the authentication endpoints", "Configuration file for database connections", "Coding style guidelines for the project").
 
 Respond with ONLY the description text, no additional formatting, preamble, or explanation.
 
@@ -141,6 +145,10 @@ File: ${fileName}${truncated ? ' (truncated)' : ''}
 --- FILE CONTENT ---
 ${contentToAnalyze}`;
 
+      // Load language instruction from settings
+      const languageInstruction = await getLanguageInstruction(settingsService);
+      const prompt = prependLanguageInstruction(basePrompt, languageInstruction);
+
       // Use the file's directory as the working directory
       const cwd = path.dirname(resolvedPath);
 

apps/server/src/routes/context/routes/describe-image.ts

@@ -19,7 +19,11 @@ import { simpleQuery } from '../../../providers/simple-query-service.js';
 import * as secureFs from '../../../lib/secure-fs.js';
 import * as path from 'path';
 import type { SettingsService } from '../../../services/settings-service.js';
-import { getAutoLoadClaudeMdSetting } from '../../../lib/settings-helpers.js';
+import {
+  getAutoLoadClaudeMdSetting,
+  getLanguageInstruction,
+} from '../../../lib/settings-helpers.js';
+import { prependLanguageInstruction } from '@automaker/prompts';
 
 const logger = createLogger('DescribeImage');
 
@@ -279,12 +283,16 @@ export function createDescribeImageHandler(
       logger.info(`[${requestId}] Using model: ${model}`);
 
       // Build the instruction text
-      const instructionText =
+      const baseInstructionText =
         `Describe this image in 1-2 sentences suitable for use as context in an AI coding assistant. ` +
         `Focus on what the image shows and its purpose (e.g., "UI mockup showing login form with email/password fields", ` +
         `"Architecture diagram of microservices", "Screenshot of error message in terminal").\n\n` +
         `Respond with ONLY the description text, no additional formatting, preamble, or explanation.`;
 
+      // Load language instruction from settings
+      const languageInstruction = await getLanguageInstruction(settingsService);
+      const instructionText = prependLanguageInstruction(baseInstructionText, languageInstruction);
+
       // Build prompt based on provider capability
       // Some providers (like Cursor) may not support image content blocks
       let prompt: string | Array<{ type: string; text?: string; source?: object }>;

apps/server/src/routes/features/index.ts

@@ -4,6 +4,7 @@
 
 import { Router } from 'express';
 import { FeatureLoader } from '../../services/feature-loader.js';
+import type { SettingsService } from '../../services/settings-service.js';
 import { validatePathParams } from '../../middleware/validate-paths.js';
 import { createListHandler } from './routes/list.js';
 import { createGetHandler } from './routes/get.js';
@@ -15,7 +16,10 @@ import { createDeleteHandler } from './routes/delete.js';
 import { createAgentOutputHandler, createRawOutputHandler } from './routes/agent-output.js';
 import { createGenerateTitleHandler } from './routes/generate-title.js';
 
-export function createFeaturesRoutes(featureLoader: FeatureLoader): Router {
+export function createFeaturesRoutes(
+  featureLoader: FeatureLoader,
+  settingsService?: SettingsService
+): Router {
   const router = Router();
 
   router.post('/list', validatePathParams('projectPath'), createListHandler(featureLoader));
@@ -35,7 +39,7 @@ export function createFeaturesRoutes(featureLoader: FeatureLoader): Router {
   router.post('/delete', validatePathParams('projectPath'), createDeleteHandler(featureLoader));
   router.post('/agent-output', createAgentOutputHandler(featureLoader));
   router.post('/raw-output', createRawOutputHandler(featureLoader));
-  router.post('/generate-title', createGenerateTitleHandler());
+  router.post('/generate-title', createGenerateTitleHandler(settingsService));
 
   return router;
 }

apps/server/src/routes/features/routes/generate-title.ts

@@ -8,7 +8,10 @@
 import type { Request, Response } from 'express';
 import { createLogger } from '@automaker/utils';
 import { CLAUDE_MODEL_MAP } from '@automaker/model-resolver';
+import { prependLanguageInstruction } from '@automaker/prompts';
 import { simpleQuery } from '../../../providers/simple-query-service.js';
+import type { SettingsService } from '../../../services/settings-service.js';
+import { getLanguageInstruction } from '../../../lib/settings-helpers.js';
 
 const logger = createLogger('GenerateTitle');
 
@@ -35,7 +38,9 @@ Rules:
 - No quotes, periods, or extra formatting
 - Capture the essence of the feature in a scannable way`;
 
-export function createGenerateTitleHandler(): (req: Request, res: Response) => Promise<void> {
+export function createGenerateTitleHandler(
+  settingsService?: SettingsService
+): (req: Request, res: Response) => Promise<void> {
   return async (req: Request, res: Response): Promise<void> => {
     try {
       const { description } = req.body as GenerateTitleRequestBody;
@@ -61,11 +66,15 @@ export function createGenerateTitleHandler(): (req: Request, res: Response) => P
 
       logger.info(`Generating title for description: ${trimmedDescription.substring(0, 50)}...`);
 
+      // Load language instruction from settings
+      const languageInstruction = await getLanguageInstruction(settingsService);
+      const effectiveSystemPrompt = prependLanguageInstruction(SYSTEM_PROMPT, languageInstruction);
+
       const userPrompt = `Generate a concise title for this feature:\n\n${trimmedDescription}`;
 
       // Use simpleQuery - provider abstraction handles all the streaming/extraction
       const result = await simpleQuery({
-        prompt: `${SYSTEM_PROMPT}\n\n${userPrompt}`,
+        prompt: `${effectiveSystemPrompt}\n\n${userPrompt}`,
         model: CLAUDE_MODEL_MAP.haiku,
         cwd: process.cwd(),
         maxTurns: 1,