AstrologerAI: an AI astrology app localized into 52 languages
How the AstrologerAI app translated its entire experience into 52 languages with LocalePack — 6.3M tokens for $58.73 — to reach a worldwide audience in their own language.
One format, every major browser
AI localization for browser extensions
Upload your source messages.json, pick target languages, pay once, and download a ready-to-ship _locales ZIP.
Placeholder-safe translations
WebExtension messages.json compliant
Transparent pricing
How it works
Three simple steps to localize your browser extension. Translations run after payment—we queue jobs and generate the ZIP in minutes.
01
Upload
Drop your source messages.json file. We parse it instantly and validate the browser extension format.
02
Select languages & see price
Choose from 52 languages. See transparent pricing based on your file size before you pay.
03
Download ZIP
Pay once via Stripe. We generate all _locales/{lang}/messages.json files and bundle them into a ZIP.
Live pricing demo
Transparent pricing estimator
See exactly what you'll pay before uploading. Final quote is computed after upload based on string length and languages selected.
1. Upload file
Drop messages.json here
or click to browse
WebExtension messages.json format. Max 500KB.
2. Select languages
|
3 of 55 languages selected
3. Your estimate
Languages selected3
Final price calculated after file upload on checkout page
One-time payment • No subscription
Built for developers
Purpose-built for browser extension locale format. Not a generic translation tool.
WebExtension format aware
Built specifically for browser extension messages.json structure with message, description, and placeholders support.
Placeholder protection
Preserves $PLACEHOLDER$ syntax exactly as-is. Your variables stay intact across all languages.
Description context
We read your description fields and use them as context hints for more accurate AI translations.
ZIP export ready
Download a ZIP with correct _locales/{lang}/messages.json folder structure. Drop it into your extension.
Parallel processing
All languages are translated simultaneously. Most jobs complete in under 5 minutes.
One-time payment
No subscriptions, no monthly fees. Pay once per job, download forever.
How WebExtension extension i18n works
Every major browser reads the same _locales/{locale}/messages.json structure. Chrome, Edge and Opera expose the chrome.i18n namespace; Firefox and Safari expose browser.i18n. The file format, the placeholder syntax and the default_locale requirement are identical across all of them, which is why a single translated folder ships everywhere.
_locales/ folder structure
_locales/
├── en/
│ └── messages.json ← default_locale
├── de/
│ └── messages.json
├── fr/
│ └── messages.json
└── ja/
└── messages.jsonmessages.json
{
"appName": {
"message": "My Extension",
"description": "Extension name"
},
"greeting": {
"message": "Hello, $USER$!",
"placeholders": {
"user": { "content": "$1" }
}
}
}Runtime API
chrome.i18n / browser.i18nExample call
getMessage("key")Required in manifest
"default_locale"In-extension strings come from _locales/. Store listing copy is managed separately in each store's own dashboard — translating one does not translate the other.
What actually differs between browsers
The messages.json format is shared across every major browser. Only four things vary, and none of them require re-translating your strings.
- Runtime namespace
- Chrome, Edge, and Opera expose chrome.i18n. Firefox and Safari expose browser.i18n. The method names and arguments are otherwise the same.
- Folder location
- Most browsers read _locales/ from the extension root. Build frameworks move it: WXT emits public/_locales/, and Plasmo reads locales/ rather than _locales/.
- Store listing text
- In-extension strings come from _locales/. Store listing copy does not — Chrome Web Store, AMO, and App Store Connect each manage listing translations in their own dashboard.
- Locale-code lists
- Chromium browsers accept a fixed set of underscore-separated codes and silently ignore anything else. Check your codes before shipping rather than after.
One translated _locales/ folder covers Chrome, Firefox, Edge, Opera, and Safari. The porting work is in the build, never in the strings.
Why not just use generic tools?
General-purpose translation tools don't understand browser extension format.
LocalePack | Manual translation | Generic TMS | |
|---|---|---|---|
| Setup time | 2 minutes | Hours per language | 30+ minutes |
| Cost transparency | |||
| WebExtension format safety | |||
| Placeholder protection | |||
| Speed (52 languages) | < 5 min | Weeks | Hours |
| Best for | Cross-browser extensions | Small projects | Enterprise web apps |
Success Cases
Real projects that used LocalePack to reach a global audience in up to 52 languages.
DevToys.pro: 400% international traffic growth across 52 languages
How the DevToys.pro web app translated its entire UI into 52 languages with LocalePack — 5.8M tokens for $58.44 — and quadrupled its international organic traffic.
DevToys New Tab: a Chrome extension localized UI + store listing in 52 languages
How the DevToys New Tab Chrome extension localized both its in-extension UI and its Chrome Web Store listing into 52 languages to reach a global audience.
LocalePack localized itself into 52 languages — with LocalePack
We used our own tool to translate the entire LocalePack site into 52 languages — 2.9M tokens for $27.37 — so developers worldwide find us in their own language.
Trusted by extension developers
“Saved me hours of tedious work. Uploaded my messages.json, got back perfect translations in the exact format I needed.”
Sarah K.
Indie dev, AdBlock extension
“We ship the same _locales folder to Chrome, Firefox and Edge. One translation pass covers all three.”
Marcus T.
Extension maintainer
“Transparent pricing was the selling point. I knew exactly what I'd pay before uploading anything.”
Dev J.
Open source contributor
52
Locales supported
100%
Placeholder-safe output
ZIP
Ready to ship
Frequently asked questions
Everything you need to know about LocalePack.
Related developer guides
Deep dives on the formats, APIs and errors behind this page — written for developers, not translators.
messages.json format explained (with placeholders)
A complete reference for the WebExtension messages.json format: the message, description, and placeholders fields, $PLACEHOLDER$ syntax, $1 positional substitutions, and common mistakes.
WXT i18n: @wxt-dev/i18n and messages.json
How @wxt-dev/i18n compiles YAML, JSON, JSONC, JSON5 and TOML message files into standard _locales/{lang}/messages.json — setup, nested keys, plurals, substitutions, type safety, and how to translate a WXT project.
Plasmo i18n: the locales/ folder gotcha
Plasmo does not read _locales/ at the project root. The three paths it does accept, where default_locale actually lives, the alphabetical-default trap, and how to place a translated _locales ZIP correctly.
Adding i18n to a CRXJS extension
CRXJS ships no i18n helper and its docs have no i18n page. Here is the working pattern: put _locales under public/, declare default_locale in manifest.config.ts, and call chrome.i18n directly.