diff --git a/src/core/prompts/__tests__/sections.test.ts b/src/core/prompts/__tests__/sections.test.ts
index 2716f610f49..8ace0c6ff2c 100644
--- a/src/core/prompts/__tests__/sections.test.ts
+++ b/src/core/prompts/__tests__/sections.test.ts
@@ -13,7 +13,7 @@ describe("addCustomInstructions", () => {
 		)
 
 		expect(result).toContain("Language Preference:")
-		expect(result).toContain('You should always speak and think in the "fr" language')
+		expect(result).toContain('You should always speak and think in the "Français" (fr) language')
 	})
 
 	test("works without vscode language", async () => {
diff --git a/src/core/prompts/sections/__tests__/custom-instructions.test.ts b/src/core/prompts/sections/__tests__/custom-instructions.test.ts
index 1922a22efcf..4dbb51c845b 100644
--- a/src/core/prompts/sections/__tests__/custom-instructions.test.ts
+++ b/src/core/prompts/sections/__tests__/custom-instructions.test.ts
@@ -117,7 +117,8 @@ describe("addCustomInstructions", () => {
 		)
 
 		expect(result).toContain("Language Preference:")
-		expect(result).toContain("es")
+		expect(result).toContain("Español") // Check for language name
+		expect(result).toContain("(es)") // Check for language code in parentheses
 		expect(result).toContain("Global Instructions:\nglobal instructions")
 		expect(result).toContain("Mode-specific Instructions:\nmode instructions")
 		expect(result).toContain("Rules from .clinerules-test-mode:\nmode specific rules")
@@ -145,6 +146,22 @@ describe("addCustomInstructions", () => {
 		expect(result).not.toContain("Rules from .clinerules-test-mode")
 	})
 
+	it("should handle unknown language codes properly", async () => {
+		mockedFs.readFile.mockRejectedValue({ code: "ENOENT" })
+
+		const result = await addCustomInstructions(
+			"mode instructions",
+			"global instructions",
+			"/fake/path",
+			"test-mode",
+			{ language: "xyz" }, // Unknown language code
+		)
+
+		expect(result).toContain("Language Preference:")
+		expect(result).toContain('"xyz" (xyz) language') // For unknown codes, the code is used as the name too
+		expect(result).toContain("Global Instructions:\nglobal instructions")
+	})
+
 	it("should throw on unexpected errors", async () => {
 		const error = new Error("Permission denied") as NodeJS.ErrnoException
 		error.code = "EPERM"
diff --git a/src/core/prompts/sections/custom-instructions.ts b/src/core/prompts/sections/custom-instructions.ts
index 04ef5b06c95..f076777585d 100644
--- a/src/core/prompts/sections/custom-instructions.ts
+++ b/src/core/prompts/sections/custom-instructions.ts
@@ -1,6 +1,7 @@
 import fs from "fs/promises"
 import path from "path"
 import * as vscode from "vscode"
+import { LANGUAGES } from "../../../shared/language"
 
 async function safeReadFile(filePath: string): Promise<string> {
 	try {
@@ -47,8 +48,9 @@ export async function addCustomInstructions(
 
 	// Add language preference if provided
 	if (options.language) {
+		const languageName = LANGUAGES[options.language] || options.language
 		sections.push(
-			`Language Preference:\nYou should always speak and think in the "${options.language}" language unless the user gives you instructions below to do otherwise.`,
+			`Language Preference:\nYou should always speak and think in the "${languageName}" (${options.language}) language unless the user gives you instructions below to do otherwise.`,
 		)
 	}
 
diff --git a/src/shared/language.ts b/src/shared/language.ts
index b5cb4228b5c..c7bc53b00c7 100644
--- a/src/shared/language.ts
+++ b/src/shared/language.ts
@@ -1,3 +1,24 @@
+/**
+ * Language name mapping from ISO codes to full language names
+ */
+export const LANGUAGES: Record<string, string> = {
+	ca: "Català",
+	de: "Deutsch",
+	en: "English",
+	es: "Español",
+	fr: "Français",
+	hi: "हिन्दी",
+	it: "Italiano",
+	ja: "日本語",
+	ko: "한국어",
+	pl: "Polski",
+	"pt-BR": "Português",
+	tr: "Türkçe",
+	vi: "Tiếng Việt",
+	"zh-CN": "简体中文",
+	"zh-TW": "繁體中文",
+}
+
 /**
  * Formats a VSCode locale string to ensure the region code is uppercase.
  * For example, transforms "en-us" to "en-US" or "fr-ca" to "fr-CA".
diff --git a/webview-ui/src/components/settings/LanguageSettings.tsx b/webview-ui/src/components/settings/LanguageSettings.tsx
index 74f35b891ae..7e6d1ea9bcb 100644
--- a/webview-ui/src/components/settings/LanguageSettings.tsx
+++ b/webview-ui/src/components/settings/LanguageSettings.tsx
@@ -4,29 +4,12 @@ import { Globe } from "lucide-react"
 
 import { cn } from "@/lib/utils"
 import { Select, SelectContent, SelectGroup, SelectItem, SelectTrigger, SelectValue } from "@/components/ui"
+import { LANGUAGES } from "../../../../src/shared/language"
 
 import { SetCachedStateField } from "./types"
 import { SectionHeader } from "./SectionHeader"
 import { Section } from "./Section"
 
-const LANGUAGES: Record<string, string> = {
-	ca: "Català",
-	de: "Deutsch",
-	en: "English",
-	es: "Español",
-	fr: "Français",
-	hi: "हिन्दी",
-	it: "Italiano",
-	ja: "日本語",
-	ko: "한국어",
-	pl: "Polski",
-	"pt-BR": "Português",
-	tr: "Türkçe",
-	vi: "Tiếng Việt",
-	"zh-CN": "简体中文",
-	"zh-TW": "繁體中文",
-}
-
 type LanguageSettingsProps = HTMLAttributes<HTMLDivElement> & {
 	language: string
 	setCachedStateField: SetCachedStateField<"language">