diff --git a/.changeset/skip-non-language-dirs.md b/.changeset/skip-non-language-dirs.md
new file mode 100644
index 000000000..3fa7ef511
--- /dev/null
+++ b/.changeset/skip-non-language-dirs.md
@@ -0,0 +1,37 @@
+---
+"@alauda/doom": patch
+---
+
+Only a supported language's directory is a language. Any other directory under
+the docs root is now skipped with a warning instead of failing the build.
+
+Every directory directly under the docs root used to become a language, apart
+from `dist`, `node_modules`, `public` and `shared`. Each language gets a
+`/<lang>/products` page whose heading comes from doom's word list, and the word
+list only has `en`, `zh` and `ru`. So when `tektoncd-operator` added a shell
+script under `docs/scripts/`, `scripts` became a language, and every docs build
+of both its branches failed from then on (65 runs over two days, none green)
+with an error that says nothing about the directory:
+
+```text
+Page "/scripts/products" SSG rendering failed.
+TypeError: Cannot read properties of undefined (reading 'all_product_documentation')
+```
+
+Nor could a site work around it: there is no option to name the languages, and
+a `themeConfig.locales` list in the config is appended to the detected one
+rather than replacing it.
+
+A directory is now a language only if its name is one of
+`SUPPORTED_LANGUAGES`, the list `doom lint` and `doom translate` already use.
+Any other directory is left out of the site the way `shared/` is — none of its
+files becomes a page — and the build says which one it skipped:
+
+```text
+Skipped `docs/scripts`: not a language directory (doom builds en, zh, ru), so no pages are built from it, like `shared`
+```
+
+`-I` / `-E` still pick the languages first; a directory they leave out is
+skipped silently, as before. The same rule covers a directory of pages in a
+language doom does not support, such as `docs/ja/`: its pages are not built, and
+the warning is the only sign of it.
diff --git a/packages/doom/src/cli/load-config.ts b/packages/doom/src/cli/load-config.ts
index a8ca3ed73..6183b71ff 100644
--- a/packages/doom/src/cli/load-config.ts
+++ b/packages/doom/src/cli/load-config.ts
@@ -44,7 +44,9 @@ import {
 } from '../plugins/index.ts'
 import {
   isExplicitlyUnversioned,
+  Language,
   normalizeSlash,
+  SUPPORTED_LANGUAGES,
   UNVERSIONED,
   type DoomSite,
 } from '../shared/index.ts'
@@ -192,6 +194,18 @@ const getCommonConfig = async ({
           continue
         }
       }
+      // Only a language doom supports is a language. Any other directory, a
+      // `scripts/` or `images/` say, used to become one and get a
+      // `/<name>/products` page with no words to render, which failed the
+      // build. It is left out of the site like `shared/` instead: it stays in
+      // `allLanguages`, so it ends up in `unusedLanguages` and its routes are
+      // excluded below.
+      if (!Object.hasOwn(Language, name)) {
+        logger.warn(
+          `Skipped \`${cyan(path.relative(process.cwd(), path.join(root, name)))}\`: not a language directory (doom builds ${SUPPORTED_LANGUAGES.join(', ')}), so no pages are built from it, like \`shared\``,
+        )
+        continue
+      }
       locales.push({
         lang: name,
         label: name,
diff --git a/packages/doom/test/cli/load-config.spec.ts b/packages/doom/test/cli/load-config.spec.ts
new file mode 100644
index 000000000..91c5b8aa2
--- /dev/null
+++ b/packages/doom/test/cli/load-config.spec.ts
@@ -0,0 +1,185 @@
+import fs from 'node:fs/promises'
+import os from 'node:os'
+import path from 'node:path'
+
+import { logger } from '@rspress/core'
+import { afterEach, beforeEach, describe, expect, rs, test } from '@rstest/core'
+
+import { loadConfig } from '#cli/load-config.ts'
+import { TRANSLATIONS } from '#runtime/translation.ts'
+import { SUPPORTED_LANGUAGES } from '#shared/constants.ts'
+
+/**
+ * Every directory directly under the docs root used to become a language,
+ * apart from `dist`, `node_modules`, `public` and `shared`. Each language gets
+ * a `/<lang>/products` page whose heading comes from doom's word list, and the
+ * word list only has the supported languages — so a site that added
+ * `docs/scripts/` for a shell script failed every build with
+ *
+ *     Page "/scripts/products" SSG rendering failed.
+ *     TypeError: Cannot read properties of undefined (reading 'all_product_documentation')
+ *
+ * A directory is now a language only if its name is one of
+ * `SUPPORTED_LANGUAGES`. Any other directory is left out of the site the way
+ * `shared/` is, and a warning names it.
+ */
+describe('language directories', () => {
+  let root: string
+  let warnings: string[]
+
+  beforeEach(async () => {
+    root = await fs.mkdtemp(path.join(os.tmpdir(), 'doom-locales-'))
+    // A config of its own, so `loadConfig` never falls back to the one in the
+    // working directory, which is this repository's own `doom.config.yml`.
+    await fs.writeFile(path.join(root, 'doom.config.yml'), 'title: Test\n')
+    warnings = []
+    rs.spyOn(logger, 'warn').mockImplementation((message) => {
+      warnings.push(String(message))
+    })
+  })
+
+  afterEach(async () => {
+    rs.restoreAllMocks()
+    await fs.rm(root, { recursive: true, force: true })
+  })
+
+  const write = async (files: Record<string, string>) => {
+    for (const [file, content] of Object.entries(files)) {
+      const filePath = path.join(root, file)
+      await fs.mkdir(path.dirname(filePath), { recursive: true })
+      await fs.writeFile(filePath, content)
+    }
+  }
+
+  const load = async (options?: { include?: string[]; exclude?: string[] }) => {
+    const { config } = await loadConfig(root, options)
+    return {
+      config,
+      langs: (config.themeConfig?.locales ?? []).map(({ lang }) => lang).sort(),
+      excluded: config.route?.exclude ?? [],
+    }
+  }
+
+  // The warning shows the directory the way the user would type it.
+  const shown = (dir: string) =>
+    path.relative(process.cwd(), path.join(root, dir))
+
+  test('a directory of scripts beside the languages is not a language', async () => {
+    await write({
+      'en/index.md': '# Home\n',
+      'zh/index.md': '# 首页\n',
+      'scripts/check-branding.sh': 'echo ok\n',
+    })
+
+    const { config, langs, excluded } = await load()
+
+    expect(langs).toEqual(['en', 'zh'])
+    expect(excluded).toContain('scripts/**/*')
+
+    // The page that crashed: without a `scripts` language there is no
+    // `/scripts/products` to render.
+    const global = config.plugins?.find(({ name }) => name === 'doom-global')
+    const pages = await global?.addPages?.(config, true)
+    expect(pages?.map(({ routePath }) => routePath).sort()).toEqual([
+      '/login',
+      '/products',
+      '/zh/login',
+      '/zh/products',
+    ])
+
+    expect(warnings).toHaveLength(1)
+    expect(warnings[0]).toContain(shown('scripts'))
+  })
+
+  test('a directory of images is not a language', async () => {
+    await write({
+      'en/index.md': '# Home\n',
+      'images/diagram.png': 'not really a png',
+    })
+
+    const { langs, excluded } = await load()
+
+    expect(langs).toEqual(['en'])
+    expect(excluded).toContain('images/**/*')
+  })
+
+  test('pages under a language doom does not support are left out with a warning, not an error', async () => {
+    // Skipped like any other non-language directory, and the build goes on.
+    // The warning is the only sign that these pages are not on the site, so it
+    // has to name the directory.
+    await write({
+      'en/index.md': '# Home\n',
+      'ja/index.md': '# ホーム\n',
+    })
+
+    const { langs, excluded } = await load()
+
+    expect(langs).toEqual(['en'])
+    expect(excluded).toContain('ja/**/*')
+    expect(warnings).toHaveLength(1)
+    expect(warnings[0]).toContain(shown('ja'))
+  })
+
+  test('`-I` picks languages first, and the directories it leaves out are skipped silently as before', async () => {
+    await write({
+      'en/index.md': '# Home\n',
+      'zh/index.md': '# 首页\n',
+      'scripts/check-branding.sh': 'echo ok\n',
+    })
+
+    const { langs, excluded } = await load({ include: ['en'] })
+
+    expect(langs).toEqual(['en'])
+    expect(excluded).toEqual(
+      expect.arrayContaining(['zh/**/*', 'scripts/**/*']),
+    )
+    expect(warnings).toEqual([])
+  })
+
+  test('`shared` and `public` hold files without becoming languages', async () => {
+    await write({
+      'en/index.md': '# Home\n',
+      'shared/snippet.mdx': 'Shared text\n',
+      'public/en/notes.md': '# Notes\n',
+    })
+
+    const { langs } = await load()
+
+    expect(langs).toEqual(['en'])
+    expect(warnings).toEqual([])
+  })
+
+  test('each supported language becomes a language with its display name', async () => {
+    await write(
+      Object.fromEntries(
+        SUPPORTED_LANGUAGES.map((lang) => [`${lang}/index.md`, '# Home\n']),
+      ),
+    )
+
+    const { config } = await loadConfig(root)
+    const locales = config.themeConfig?.locales ?? []
+
+    expect(locales).toHaveLength(SUPPORTED_LANGUAGES.length)
+    for (const { lang, label } of locales) {
+      // Without a display name the label falls back to the directory name.
+      expect(label).not.toBe(lang)
+    }
+    expect(warnings).toEqual([])
+  })
+})
+
+/**
+ * Whether a directory is a language is now decided by `SUPPORTED_LANGUAGES`, so
+ * the word list has to cover exactly those languages. A language added to the
+ * word list alone would be skipped as a non-language directory; one added to
+ * `SUPPORTED_LANGUAGES` alone would render its products page from `undefined`,
+ * the crash described above.
+ */
+describe('supported languages', () => {
+  test('are exactly the languages with a word list', () => {
+    expect(SUPPORTED_LANGUAGES.length).toBeGreaterThan(0)
+    expect(Object.keys(TRANSLATIONS).sort()).toEqual(
+      [...SUPPORTED_LANGUAGES].sort(),
+    )
+  })
+})