diff --git a/lib/core/__tests__/__snapshots__/utils.test.js.snap b/lib/core/__tests__/__snapshots__/utils.test.js.snap
index a7eb240a4fcb..d38a322ff622 100644
--- a/lib/core/__tests__/__snapshots__/utils.test.js.snap
+++ b/lib/core/__tests__/__snapshots__/utils.test.js.snap
@@ -1,6 +1,6 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
-exports[`utils extractBlogPostBeforeTruncate 1`] = `
+exports[`core utils extractBlogPostBeforeTruncate 1`] = `
 "---
 title: Truncation Example
 ---
@@ -12,7 +12,7 @@ Even this.
 "
 `;
 
-exports[`utils extractBlogPostBeforeTruncate 2`] = `
+exports[`core utils extractBlogPostBeforeTruncate 2`] = `
 "---
 title: Non-truncation Example
 ---
@@ -29,7 +29,7 @@ And this too.
 "
 `;
 
-exports[`utils extractBlogPostSummary 1`] = `
+exports[`core utils extractBlogPostSummary 1`] = `
 "---
 title: Truncation Example
 ---
@@ -48,7 +48,7 @@ Or this.
 "
 `;
 
-exports[`utils extractBlogPostSummary 2`] = `
+exports[`core utils extractBlogPostSummary 2`] = `
 "---
 title: Non-truncation Example
 ---
diff --git a/lib/core/__tests__/utils.test.js b/lib/core/__tests__/utils.test.js
index 04ccef614e20..a313cf9a3bf1 100644
--- a/lib/core/__tests__/utils.test.js
+++ b/lib/core/__tests__/utils.test.js
@@ -19,7 +19,7 @@ const blogPostWithoutTruncateContents = fs.readFileSync(
   'utf8'
 );
 
-describe('utils', () => {
+describe('core utils', () => {
   test('blogPostHasTruncateMarker', () => {
     expect(utils.blogPostHasTruncateMarker(blogPostWithTruncateContents)).toBe(
       true
diff --git a/lib/server/__tests__/utils.test.js b/lib/server/__tests__/utils.test.js
index 8459edcd4018..42c7280cf631 100644
--- a/lib/server/__tests__/utils.test.js
+++ b/lib/server/__tests__/utils.test.js
@@ -8,6 +8,24 @@ const path = require('path');
 const fs = require('fs');
 const utils = require('../utils');
 
+jest.mock('../env', () => ({
+  translation: {
+    enabled: true,
+    enabledLanguages: () => [
+      {
+        enabled: true,
+        name: 'English',
+        tag: 'en',
+      },
+      {
+        enabled: true,
+        name: '日本語',
+        tag: 'ja',
+      },
+    ],
+  },
+}));
+
 describe('server utils', () => {
   test('minify css', () => {
     const testCss = fs.readFileSync(
@@ -21,4 +39,44 @@ describe('server utils', () => {
     utils.minifyCss(testCss).then(css => expect(css).toMatchSnapshot());
     utils.minifyCss(notCss).catch(e => expect(e).toMatchSnapshot());
   });
+
+  test('getLanguage', () => {
+    const testDocEnglish = path.join('translated_docs', 'en', 'test.md');
+    const testDocJapanese = path.join('translated_docs', 'ja', 'test.md');
+    const testDocJapaneseInSubfolder = path.join(
+      'translated_docs',
+      'ja',
+      'en',
+      'test.md'
+    );
+    const testDocInSubfolder = path.join('docs', 'ro', 'test.md');
+    const testDocNoLanguage = path.join('docs', 'test.md');
+    expect(utils.getLanguage(testDocEnglish, 'translated_docs')).toBe('en');
+    expect(utils.getLanguage(testDocJapanese, 'translated_docs')).toBe('ja');
+    expect(
+      utils.getLanguage(testDocJapaneseInSubfolder, 'translated_docs')
+    ).toBe('ja');
+    expect(utils.getLanguage(testDocInSubfolder, 'docs')).toBeNull();
+    expect(utils.getLanguage(testDocNoLanguage, 'docs')).toBeNull();
+  });
+
+  test('getSubdir', () => {
+    const docA = path.join('docs', 'endiliey', 'a.md');
+    const docB = path.join('docs', 'nus', 'hackers', 'b.md');
+    const docC = path.join('docs', 'c.md');
+    const docD = path.join('website', 'translated_docs', 'wow', 'd.md');
+    const docE = path.join('website', 'translated_docs', 'lol', 'lah', 'e.md');
+    const docsDir = path.join('docs');
+    const translatedDir = path.join('website', 'translated_docs');
+    expect(utils.getSubDir(docA, docsDir)).toEqual('endiliey');
+    expect(utils.getSubDir(docA, translatedDir)).toBeNull();
+    expect(utils.getSubDir(docB, docsDir)).toEqual('nus/hackers');
+    expect(utils.getSubDir(docB, translatedDir)).toBeNull();
+    expect(utils.getSubDir(docC, docsDir)).toBeNull();
+    expect(utils.getSubDir(docC, translatedDir)).toBeNull();
+    expect(utils.getSubDir(docD, docsDir)).toBeNull();
+    expect(utils.getSubDir(docD, translatedDir)).toEqual('wow');
+    expect(utils.getSubDir(docE, docsDir)).toBeNull();
+    expect(utils.getSubDir(docE, translatedDir)).toEqual('lol/lah');
+  });
 });
diff --git a/lib/server/utils.js b/lib/server/utils.js
index c10814d784c8..a252eb1f99ef 100644
--- a/lib/server/utils.js
+++ b/lib/server/utils.js
@@ -9,23 +9,14 @@ const cssnano = require('cssnano');
 const path = require('path');
 const escapeStringRegexp = require('escape-string-regexp');
 
-// Return the subdirectory path from a reference directory
-// Example:
-//  (file: 'docs/projectA/test.md', refDir: 'docs')
-//  returns 'projectA'
 function getSubDir(file, refDir) {
-  let subDir = path.dirname(path.relative(refDir, file));
-  subDir = subDir.replace('\\', '/');
-  return subDir !== '.' ? subDir : null;
+  const subDir = path.dirname(path.relative(refDir, file)).replace('\\', '/');
+  return subDir !== '.' && !subDir.includes('..') ? subDir : null;
 }
 
-// Get the corresponding enabled language locale of a file.
-// Example:
-//  (file: '/website/translated_docs/ko/projectA/test.md', refDir: 'website/translated_docs')
-//  returns 'ko'
 function getLanguage(file, refDir) {
   const regexSubFolder = new RegExp(
-    `/${escapeStringRegexp(path.basename(refDir))}/(.*)/.*/`
+    `${escapeStringRegexp(path.basename(refDir))}/(.*?)/.*`
   );
   const match = regexSubFolder.exec(file);