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Paraglide JS

Compiler-based internationalization for SvelteKit. Compiles message files into type-safe functions with IntelliSense.

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What is it?

Compiler-based internationalization for SvelteKit. Compiles message files into type-safe functions with IntelliSense. Minimal runtime (~1-2KB), full tree-shaking, no hydration mismatch.

What is it for?

  • Compile-time translation compilation (messages → typed functions)
  • Type-safe message keys with autocomplete
  • Per-page tree-shaking (unused messages eliminated)
  • URL-based locale routing via reroute hook
  • Zero hydration mismatch (locale resolved before render)

Why was it chosen?

Aspect Paraglide v2 svelte-i18n typesafe-i18n
Bundle ~1-2KB 14KB (FormatJS) ~1KB
Type safety Full (typed functions) None (string keys) Full
Tree-shaking Per-page No (all together) Yes
Hydration No mismatch Risk of mismatch No mismatch
SvelteKit support Official (npx sv add) Community Community
Routing reroute hook (no params) [[lang]] param Custom
Maintenance Active (Inlang team) "Due for reworking" Abandoned (creator passed)

Key advantages:

  • Smallest bundle for production (~1-2KB vs 14KB)
  • Full type safety eliminates missing translation runtime errors
  • Official SvelteKit integration auto-configures hooks and Vite plugin
  • No server/client locale mismatch (URL/cookie resolved before render)
  • Per-page tree-shaking reduces bundle per route

Why not svelte-i18n? 14KB runtime, no type safety, hydration mismatch risk, maintainer uncertainty ("due to some reworking").

Why not typesafe-i18n? Creator passed away in 2023. Library effectively abandoned.

Known limitations

Language switching:

  • Requires full page reload (use data-sveltekit-reload on links)
  • No runtime switching without reload

Bundle splitting:

  • All locales compiled together (not split per language)
  • Tree-shaken per page (unused messages eliminated)
  • For 20+ languages, bundle grows (reconsider if per-locale splitting ships)

ICU MessageFormat:

  • Supported but syntax differs slightly from FormatJS
  • Pluralization and interpolation fully supported

Locale strategy:

  • Language-only codes (en, de, fr) recommended
  • Full locales (de-DE, de-AT) supported but formatting handled separately

Related

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