diff --git a/gitnexus/src/cli/index.ts b/gitnexus/src/cli/index.ts
index 4b009e4aa..0243a3d63 100644
--- a/gitnexus/src/cli/index.ts
+++ b/gitnexus/src/cli/index.ts
@@ -166,6 +166,7 @@ program
   .option('--gist', 'Publish wiki as a public GitHub Gist after generation')
   .option('-v, --verbose', 'Enable verbose output (show LLM commands and responses)')
   .option('--review', 'Stop after grouping to review module structure before generating pages')
+  .option('--lang <lang>', 'Output language for generated documentation (e.g. english, chinese, spanish, japanese)')
   .action(createLazyAction(() => import('./wiki.js'), 'wikiCommand'));
 
 program
diff --git a/gitnexus/src/cli/wiki.ts b/gitnexus/src/cli/wiki.ts
index 8d9da9572..fbba987ec 100644
--- a/gitnexus/src/cli/wiki.ts
+++ b/gitnexus/src/cli/wiki.ts
@@ -35,6 +35,7 @@ export interface WikiCommandOptions {
   review?: boolean;
   timeout?: string;
   retries?: string;
+  lang?: string;
 }
 
 /**
@@ -395,6 +396,7 @@ export const wikiCommand = async (inputPath?: string, options?: WikiCommandOptio
     force: options?.force,
     concurrency: options?.concurrency ? parseInt(options.concurrency, 10) : undefined,
     reviewOnly: options?.review,
+    lang: options?.lang,
   };
 
   const generator = new WikiGenerator(
diff --git a/gitnexus/src/core/wiki/generator.ts b/gitnexus/src/core/wiki/generator.ts
index dc9c2e74e..4d4b30572 100644
--- a/gitnexus/src/core/wiki/generator.ts
+++ b/gitnexus/src/core/wiki/generator.ts
@@ -66,6 +66,8 @@ export interface WikiOptions {
   concurrency?: number;
   /** If true, stop after building module tree for user review */
   reviewOnly?: boolean;
+  /** Output language for generated documentation (e.g. 'english', 'chinese', 'spanish') */
+  lang?: string;
 }
 
 export interface WikiMeta {
@@ -177,6 +179,15 @@ export class WikiGenerator {
     };
   }
 
+  /**
+   * Append an output-language instruction to a system prompt when --lang is set.
+   */
+  private buildSystemPrompt(base: string): string {
+    if (!this.options.lang) return base;
+    const lang = this.options.lang.trim();
+    return `${base}\n\nIMPORTANT: Write ALL documentation content in ${lang}. This includes headings, prose, code comments in examples, and diagram labels.`;
+  }
+
   /**
    * Route LLM call to the appropriate provider (OpenAI-compatible or Cursor CLI).
    */
@@ -417,7 +428,7 @@ export class WikiGenerator {
 
     const response = await this.invokeLLM(
       prompt,
-      GROUPING_SYSTEM_PROMPT,
+      this.buildSystemPrompt(GROUPING_SYSTEM_PROMPT),
       this.streamOpts('Grouping files', 15, 13),
     );
     const grouping = this.parseGroupingResponse(response.content, files);
@@ -589,7 +600,7 @@ export class WikiGenerator {
       PROCESSES: formatProcesses(processes),
     });
 
-    const response = await this.invokeLLM(prompt, MODULE_SYSTEM_PROMPT, this.streamOpts(node.name));
+    const response = await this.invokeLLM(prompt, this.buildSystemPrompt(MODULE_SYSTEM_PROMPT), this.streamOpts(node.name));
 
     // Write page with front matter
     const pageContent = sanitizeMermaidMarkdown(`# ${node.name}\n\n${response.content}`);
@@ -630,7 +641,7 @@ export class WikiGenerator {
       CROSS_PROCESSES: formatProcesses(processes),
     });
 
-    const response = await this.invokeLLM(prompt, PARENT_SYSTEM_PROMPT, this.streamOpts(node.name));
+    const response = await this.invokeLLM(prompt, this.buildSystemPrompt(PARENT_SYSTEM_PROMPT), this.streamOpts(node.name));
 
     const pageContent = sanitizeMermaidMarkdown(`# ${node.name}\n\n${response.content}`);
     await fs.writeFile(path.join(this.wikiDir, `${node.slug}.md`), pageContent, 'utf-8');
@@ -678,7 +689,7 @@ export class WikiGenerator {
 
     const response = await this.invokeLLM(
       prompt,
-      OVERVIEW_SYSTEM_PROMPT,
+      this.buildSystemPrompt(OVERVIEW_SYSTEM_PROMPT),
       this.streamOpts('Generating overview', 88),
     );