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.
Placeholder-safe messages.json translation
AI localization for messages.json files
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
messages.json input. 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
A messages.json entry pairs a key with a "message" string, an optional "description" used as translation context, and an optional "placeholders" map. LocalePack parses all three: it translates only the message text, forwards the description to the model as context, and returns $PLACEHOLDER$ and $1 substitution tokens byte-identical.
_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"The same translated messages.json drops into _locales/{locale}/ for Chrome, Firefox, Edge, Opera and Safari without further edits.
What the translator has to preserve
A messages.json entry is more than a key and a string. Getting these four pieces wrong is what breaks extensions after machine translation.
- message
- The user-visible string, and the only field that should ever change during translation.
- description
- Context for whoever — or whatever — translates the string. LocalePack feeds this to the model as translation context, so a good description measurably improves output quality.
- placeholders
- Named substitutions written as $PLACEHOLDER$ in the message, with their own content definitions. These must survive translation exactly, including the dollar signs and casing.
- Positional substitutions
- $1 through $9 map to arguments passed to getMessage(). A translator that reorders a sentence must keep these tokens intact, not renumber them.
Most generic translation tools treat $PLACEHOLDER$ and $1 as ordinary words. Once they are translated or reordered, the extension ships with broken interpolation.
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 | Any messages.json file | 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
“Our $PLACEHOLDER$ tokens came back untouched in all 52 locales. That is the whole reason we stopped scripting it ourselves.”
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.
Validate messages.json before shipping
How to catch every class of messages.json error before your users do: JSON syntax, missing required fields, missing keys across locales, malformed placeholder syntax, and manifest key mismatches.
__MSG_key__ in manifest.json explained
How the __MSG_key__ substitution syntax works in Chrome and Firefox extension manifests: which fields support it, how Chrome resolves tokens at load time, and the pitfalls that cause silent failures or upload rejections.
chrome.i18n.getMessage() returns empty
getMessage() returns an empty string when a message is missing, and logs nothing at all. Every cause of the silent empty string, how to tell it apart from undefined, and how to confirm each one.