diff --git a/external/importL10n/locales.mjs b/external/importL10n/locales.mjs
index 7883e0977..62264d3ff 100644
--- a/external/importL10n/locales.mjs
+++ b/external/importL10n/locales.mjs
@@ -14,7 +14,6 @@
  */
 
 import fs from "fs";
-import https from "https";
 import path from "path";
 
 // Fetches all languages that have an *active* translation in mozilla-central.
@@ -22,47 +21,34 @@ import path from "path";
 
 const DEFAULT_LOCALE = "en-US";
 
-const EXCLUDE_LANG_CODES = ["ca-valencia", "ja-JP-mac"];
+const EXCLUDE_LANG_CODES = new Set(["ca-valencia", "ja-JP-mac"]);
 
 function normalizeText(s) {
   return s.replaceAll(/\r\n?/g, "\n").replaceAll("\uFEFF", "");
 }
 
-function downloadLanguageCodes() {
+async function downloadLanguageCodes() {
   console.log("Downloading language codes...\n");
 
   const ALL_LOCALES =
     "https://hg.mozilla.org/mozilla-central/raw-file/tip/browser/locales/all-locales";
 
-  return new Promise(function (resolve) {
-    https.get(ALL_LOCALES, function (response) {
-      if (response.statusCode === 200) {
-        let content = "";
-        response.setEncoding("utf8");
-        response.on("data", function (chunk) {
-          content += chunk;
-        });
-        response.on("end", function () {
-          content = content.trim(); // Remove any leading/trailing white-space.
-          const langCodes = normalizeText(content).split("\n");
-          // Remove all locales that we don't want to download below.
-          for (const langCode of [DEFAULT_LOCALE, ...EXCLUDE_LANG_CODES]) {
-            const i = langCodes.indexOf(langCode);
-            if (i > -1) {
-              langCodes.splice(i, 1);
-            }
-          }
-          resolve(langCodes);
-        });
-      } else {
-        resolve([]);
-      }
-    });
-  });
+  const response = await fetch(ALL_LOCALES);
+  if (!response.ok) {
+    throw new Error(response.statusText);
+  }
+  const content = await response.text();
+
+  // Remove any leading/trailing white-space.
+  const langCodes = normalizeText(content.trim()).split("\n");
+  // Remove all locales that we don't want to download below.
+  return langCodes.filter(
+    langCode => langCode !== DEFAULT_LOCALE && !EXCLUDE_LANG_CODES.has(langCode)
+  );
 }
 
-function downloadLanguageFiles(root, langCode) {
-  console.log("Downloading " + langCode + "...");
+async function downloadLanguageFiles(root, langCode) {
+  console.log(`Downloading ${langCode}...`);
 
   // Constants for constructing the URLs. Translations are taken from the
   // Nightly channel as those are the most recent ones.
@@ -71,41 +57,27 @@ function downloadLanguageFiles(root, langCode) {
 
   // Defines which files to download for each language.
   const files = ["viewer.ftl"];
-  let downloadsLeft = files.length;
 
   const outputDir = path.join(root, langCode);
   if (!fs.existsSync(outputDir)) {
     fs.mkdirSync(outputDir);
   }
 
-  return new Promise(function (resolve) {
-    // Download the necessary files for this language.
-    files.forEach(function (fileName) {
-      const outputPath = path.join(outputDir, fileName);
-      const url =
-        MOZ_CENTRAL_ROOT + langCode + MOZ_CENTRAL_PDFJS_DIR + fileName;
+  // Download the necessary files for this language.
+  for (const fileName of files) {
+    const outputPath = path.join(outputDir, fileName);
+    const url = MOZ_CENTRAL_ROOT + langCode + MOZ_CENTRAL_PDFJS_DIR + fileName;
 
-      https.get(url, function (response) {
-        // Not all files exist for each language. Files without translations
-        // have been removed (https://bugzilla.mozilla.org/show_bug.cgi?id=1443175).
-        if (response.statusCode === 200) {
-          let content = "";
-          response.setEncoding("utf8");
-          response.on("data", function (chunk) {
-            content += chunk;
-          });
-          response.on("end", function () {
-            fs.writeFileSync(outputPath, normalizeText(content), "utf8");
-            if (--downloadsLeft === 0) {
-              resolve();
-            }
-          });
-        } else if (--downloadsLeft === 0) {
-          resolve();
-        }
-      });
-    });
-  });
+    const response = await fetch(url);
+    if (!response.ok) {
+      // Not all files exist for each language. Files without translations
+      // have been removed (https://bugzilla.mozilla.org/show_bug.cgi?id=1443175).
+      continue;
+    }
+    const content = await response.text();
+
+    fs.writeFileSync(outputPath, normalizeText(content), "utf8");
+  }
 }
 
 async function downloadL10n(root) {