Comparing Polyglot and Localize (Localize.js) for multilingual apps. Understand the difference between code-level AST detection and JavaScript proxy-based translation.
Localize (also known as Localize.js) is a website translation tool that works via a JavaScript snippet. You add their script to your site, and it detects and replaces text in the browser. Polyglot works at the code level — it scans your source files with tree-sitter AST parsing, finds hardcoded strings, and produces translation files.
The fundamental difference: Localize translates what users see in the browser. Polyglot translates what developers write in the code.
| Feature | Polyglot | Localize |
|---|---|---|
| How it works | Code-level (AST detection) | Browser-level (JS proxy) |
| String detection | AST-based in source code | Detects rendered DOM text |
| Works with SPAs | ✓Yes (native) | ✓Yes (DOM observation) |
| Works with mobile apps | Detection for React Native and Flutter (runtime support varies) | ✕No |
| Translation approach | Built-in LLM | Google/Microsoft MT + human |
| Translations in your repo | ✓Yes (JSON, YAML, ARB, .strings, XML) | No (hosted on Localize) |
| Runtime dependency | Your i18n library only | ✓Yes (JS snippet required) |
| Local preview | ✓Yes (polyglot preview) | Live on site |
| Editor integration | VS Code extension (inline diagnostics) | ✕No |
| CLI support | Primary interface | ✕No |
| Free tier | Free local scanning, 500 source strings (lifetime) | ✕No |
| Starting price | $0 | Custom pricing |
| SEO support | You manage it | Automatic (proxy) |
Competitor pricing checked September 22, 2026.
Add a script tag and Localize starts detecting text on your pages. For marketing sites and content-heavy pages, this is the fastest path to translation.
Localize's dashboard shows your website with translation overlays. Non-technical team members can edit translations while seeing exactly how they appear on the page.
Localize watches for DOM changes, so it catches dynamically rendered content better than pure proxy solutions. This makes it more viable for SPAs than server-side proxies.
Localize handles language switching, browser locale detection, and URL management automatically.
Polyglot finds hardcoded strings in your code before they're rendered, using tree-sitter AST parsing. Detection covers Next.js, Astro, SvelteKit, Vue, Angular, React Native and Flutter; runtime support varies by setup, and Next.js App Router with next-intl is the best-tested path. Scanning source can surface strings in error handlers, conditional branches, and paths that DOM observation might never see because no user triggered them.
Polyglot's fine-tuned engine scored 4.96/5 across 49 languages on our June 2026 pipeline, AI-judged — reproducible benchmark.
Polyglot's VS Code extension flags untranslated strings inline as you code, with scan-on-save and wrap actions you review before applying — you catch gaps before the page ships.
Polyglot produces translation files your own i18n library loads. Your app doesn't load a third-party script to translate the page. With Localize, if their CDN goes down or the script fails to load, your users see untranslated content.
Translations live in your git repo as catalog files — reviewable, revertable, and deployable through your existing pipeline. Localize stores translations on their servers.
With Polyglot, translations ship with your app through your i18n library. Localize's JS snippet downloads, parses, and applies translations after page load, which can cause a flash of untranslated content (FOUC).
Polyglot's detection covers React Native and Flutter; check runtime support for your setup. Localize is web-only.
Polyglot is $0 for local scanning, $49/month ($39/month billed annually) for Pro. Localize uses custom pricing that requires a sales conversation.
This is the key architectural decision:
Localize requires a JavaScript snippet in your production site. Translations are fetched and applied at runtime. This means:
Polyglot produces catalog files that ship with your app. This means:
For most developer-led teams building applications, the build-time approach is preferred. For marketing teams that need to iterate on copy in real time without developer involvement, the runtime approach has appeal.
Start in your terminal
Install the CLI, run a scan, and see exactly what you're missing. Free, no account required.