diff --git a/interface/progmem-generator.js b/interface/progmem-generator.js
index be5cead21..79f4f4f18 100644
--- a/interface/progmem-generator.js
+++ b/interface/progmem-generator.js
@@ -46,6 +46,38 @@ ${fileInfo.map((f) => `${INDENT}{"${f.uri}", "${f.mimeType}", ${f.variable}, ${f
 static constexpr size_t WWW_ASSETS_COUNT = sizeof(WWW_ASSETS) / sizeof(WWW_ASSETS[0]);
 `;
 
+// Optional locale allow-list, shared with the Vite build via VITE_APP_LOCALES
+// (e.g. "en,de,nl"). When set, locale chunks outside the list are NOT embedded
+// into firmware flash. `en` is always kept as the fallback. Unset => embed all.
+const ALL_LOCALES = [
+  'cz',
+  'de',
+  'en',
+  'fr',
+  'it',
+  'nl',
+  'no',
+  'pl',
+  'sk',
+  'sv',
+  'tr'
+];
+const localeAllowList = (process.env.VITE_APP_LOCALES || '')
+  .split(',')
+  .map((locale) => locale.trim())
+  .filter(Boolean);
+
+const isExcludedLocaleChunk = (relativeFilePath) => {
+  if (localeAllowList.length === 0) return false;
+  const base = relativeFilePath.split(sep).pop();
+  const match = /^([a-z]{2})-[A-Za-z0-9_-]+\.js$/.exec(base);
+  if (!match) return false;
+  const code = match[1];
+  // Only treat known locale codes as locale chunks; never drop the en fallback.
+  if (!ALL_LOCALES.includes(code) || code === 'en') return false;
+  return !localeAllowList.includes(code);
+};
+
 const getFilesSync = (dir, files = []) => {
   readdirSync(dir, { withFileTypes: true }).forEach((entry) => {
     const entryPath = resolve(dir, entry.name);
@@ -116,7 +148,12 @@ writeStream.write(ARDUINO_INCLUDES);
 
 const buildPath = resolve(sourcePath);
 for (const filePath of getFilesSync(buildPath)) {
-  writeFile(relative(buildPath, filePath), readFileSync(filePath));
+  const relativeFilePath = relative(buildPath, filePath);
+  if (isExcludedLocaleChunk(relativeFilePath)) {
+    console.log(`Skipping locale (not in VITE_APP_LOCALES): ${relativeFilePath}`);
+    continue;
+  }
+  writeFile(relativeFilePath, readFileSync(filePath));
 }
 
 writeStream.write(generateWWWClass());
diff --git a/interface/src/App.tsx b/interface/src/App.tsx
index 9149eb940..8db9f2f28 100644
--- a/interface/src/App.tsx
+++ b/interface/src/App.tsx
@@ -9,7 +9,7 @@ import type { Locales } from 'i18n/i18n-types';
 import { loadLocaleAsync } from 'i18n/i18n-util.async';
 import { detectLocale, navigatorDetector } from 'typesafe-i18n/detectors';
 
-const AVAILABLE_LOCALES = [
+const ALL_LOCALES = [
   'de',
   'en',
   'it',
@@ -23,6 +23,20 @@ const AVAILABLE_LOCALES = [
   'cz'
 ] as Locales[];
 
+// Optional build-time allow-list (e.g. VITE_APP_LOCALES="en,de,nl"). When unset,
+// every locale is available. `en` is always kept as the fallback locale, and the
+// progmem generator embeds the matching subset into firmware flash.
+const localeAllowList = (import.meta.env.VITE_APP_LOCALES ?? '')
+  .split(',')
+  .map((locale) => locale.trim())
+  .filter(Boolean);
+
+const AVAILABLE_LOCALES: Locales[] = localeAllowList.length
+  ? ALL_LOCALES.filter(
+      (locale) => locale === 'en' || localeAllowList.includes(locale)
+    )
+  : ALL_LOCALES;
+
 const App = memo(() => {
   const [wasLoaded, setWasLoaded] = useState(false);
   const [locale, setLocale] = useState<Locales>('en');
@@ -30,7 +44,12 @@ const App = memo(() => {
   useEffect(() => {
     const initializeLocale = async () => {
       const browserLocale = detectLocale('en', AVAILABLE_LOCALES, navigatorDetector);
-      const newLocale = (localStorage.getItem('lang') || browserLocale) as Locales;
+      const stored = localStorage.getItem('lang');
+      // Ignore a stored locale that isn't available (e.g. trimmed from this build).
+      const newLocale =
+        stored && AVAILABLE_LOCALES.includes(stored as Locales)
+          ? (stored as Locales)
+          : browserLocale;
       localStorage.setItem('lang', newLocale);
       setLocale(newLocale);
       await loadLocaleAsync(newLocale);
diff --git a/interface/src/vite-env.d.ts b/interface/src/vite-env.d.ts
index 11f02fe2a..c5d41d92f 100644
--- a/interface/src/vite-env.d.ts
+++ b/interface/src/vite-env.d.ts
@@ -1 +1,13 @@
 /// <reference types="vite/client" />
+
+interface ImportMetaEnv {
+  // Optional comma-separated allow-list of locales to ship (e.g. "en,de,nl").
+  // Unset => all locales are bundled and embedded. `en` is always kept as the
+  // fallback. Consumed by App.tsx (UI language list) and progmem-generator.js
+  // (which locale chunks get embedded into firmware flash).
+  readonly VITE_APP_LOCALES?: string;
+}
+
+interface ImportMeta {
+  readonly env: ImportMetaEnv;
+}