diff --git a/server/src/middleware/l10n.js b/server/src/middleware/l10n.js
new file mode 100644
index 0000000000..ab5acd0285
--- /dev/null
+++ b/server/src/middleware/l10n.js
@@ -0,0 +1,28 @@
+require("../logging").installConsoleHandler();
+const mozlog = require("../logging").mozlog("l10n-middleware");
+const accepts = require("accepts");
+const l10n = require("../l10n");
+
+// Get an ordered list of user-preferred locales from the Accept-Language header
+exports.getLanguages = function(req) {
+  let languages = accepts(req).languages();
+  // 'accepts' returns '*' if no Accept-Language header was passed. Use English
+  // as a default instead. #3231
+  if (languages[0] === '*') {
+    languages = ['en-US'];
+  }
+  return languages;
+};
+
+exports.l10n = function(req, res, next) {
+  l10n.init().then(() => {
+    let languages = exports.getLanguages(req);
+    req.getText = l10n.getText(languages);
+    req.userLocales = l10n.getUserLocales(languages);
+    req.messages = l10n.getStrings(languages);
+    next();
+  }).catch(err => {
+    mozlog.error("l10n-middleware-error", {msg: "Error initializing l10n", description: err});
+    process.exit(2);
+  });
+};
diff --git a/server/src/server.js b/server/src/server.js
index 15c9e7b00a..3a310c6150 100644
--- a/server/src/server.js
+++ b/server/src/server.js
@@ -1,7 +1,6 @@
 const config = require("./config").getProperties();
 require("./logging").installConsoleHandler();
 const mozlog = require("./logging").mozlog("server");
-const accepts = require("accepts");
 const path = require('path');
 const { readFileSync, existsSync } = require('fs');
 const Cookies = require("cookies");
@@ -45,7 +44,7 @@ const { captureRavenException, sendRavenMessage,
 const { errorResponse, simpleResponse, jsResponse } = require("./responses");
 const selfPackage = require("./package.json");
 const { b64EncodeJson, b64DecodeJson } = require("./b64");
-const l10n = require("./l10n");
+const { l10n } = require("./middleware/l10n");
 
 const PROXY_HEADER_WHITELIST = {
   "content-type": true,
@@ -269,18 +268,7 @@ app.use(function(req, res, next) {
   next();
 });
 
-app.use(function(req, res, next) {
-  l10n.init().then(() => {
-    const languages = accepts(req).languages();
-    req.getText = l10n.getText(languages);
-    req.userLocales = l10n.getUserLocales(languages);
-    req.messages = l10n.getStrings(languages);
-    next();
-  }).catch(err => {
-    mozlog.error("l10n-error", {msg: "Error initializing l10n", description: err});
-    process.exit(2);
-  });
-});
+app.use(l10n);
 
 app.param("id", function(req, res, next, id) {
   if (/^[a-zA-Z0-9]{16}$/.test(id)) {
diff --git a/test/server/unit/middleware/l10n-test.js b/test/server/unit/middleware/l10n-test.js
new file mode 100644
index 0000000000..44843c98fd
--- /dev/null
+++ b/test/server/unit/middleware/l10n-test.js
@@ -0,0 +1,33 @@
+const assert = require('assert');
+const l10n = require('../../../../server/src/middleware/l10n.js');
+
+/* globals describe, it */
+
+describe('l10n middleware', () => {
+  describe('getLanguage function (Accept-Language header parsing)', () => {
+    it('should return ["en-US"] if Accept-Language header is missing', () => {
+      let mockRequest = { headers: {} };
+      let results = l10n.getLanguages(mockRequest);
+      assert(results.length === 1);
+      assert.equal('en-US', results[0]);
+    });
+    it('should return ["en-US"] if Accept-Language header value is "*"', () => {
+      let mockRequest = { headers: { 'accept-language': '*' }};
+      let results = l10n.getLanguages(mockRequest);
+      assert(results.length === 1);
+      assert.equal('en-US', results[0]);
+    });
+    it('should return ["en-US"] if Accept-Language header value is "en-CA"', () => {
+      let mockRequest = { headers: { 'accept-language': 'en-CA' }};
+      let results = l10n.getLanguages(mockRequest);
+      assert(results.length === 1);
+      assert.equal('en-US', results[0]);
+    });
+    it('should return ["en-US"] if Accept-Language header value is "en"', () => {
+      let mockRequest = { headers: { 'accept-language': 'en' }};
+      let results = l10n.getLanguages(mockRequest);
+      assert(results.length === 1);
+      assert.equal('en-US', results[0]);
+    });
+  });
+});