i18n

The canonical, self-contained playbook for localizing the Inspector SPA. Every downstream i18n agent (string-finder, translator, wiring agent, browser-tester) reads this and follows it. Read the reference subfile that matches your task — don't preload all of them.

The stack is Paraglide JS 2.x (inlang message-format). English (en) is the source locale; Arabic (ar, Modern Standard) is the first target. It is already installed and wired — you add keys + wire components, you do not re-scaffold.

Scope & order (LOCKED)

This is workflow 1: strings only. Arabic strings ship into chrome that stays LTR-positioned — the full RTL layout flip is a separate, later workflow (it updates PRODUCT.md's "don't flip the whole component" principle). Your job here is accurate strings that don't visually mangle the still-LTR layout, achieved via bidi isolation (see arabic-conventions.md §8) — not a flipped layout.

Coverage order (don't get ahead of it):

1. Public surfaces first — Dashboard (dashboard_*) + Timestamps (ts_*). These are the priority.
2. User approves the public pass → then Segments (segments_*).
3. Admin is English-default, lowest priority — do it last, only when asked.

Golden rules

1. Hand-author the message JSON. NEVER round-trip through the inlang editor / Sherlock VS Code extension — they collapse the split pathPattern array into the last file and silently blank the others, and it still passes build. Edit {en,ar}.json with the Write/Edit tools only. → paraglide.md, project-conventions.md §2.
2. Keys are flat, snake_case, area-prefixed (common_ / errors_ / dashboard_ / ts_ / segments_). Paraglide flattens everything into one m.*() namespace; the prefix is the only thing stopping a title in one tab clobbering a title in another (duplicate ids resolve last-wins, silently). → project-conventions.md §1.
3. en ↔ ar files stay key-for-key identical (same id set, same order). A missing key in one locale silently drops it. Author the en key, then the ar key in the same position in the sibling file.
4. Translate chrome, never data. Reciter names, surah names (use API name_ar/name_en), Quran text/tokens/shard letters are data — never keyed. → §"don't-translate" below + arabic-conventions.md §6.
5. A Svelte file is fully runes OR fully legacy — never mix. Wire each per its mode (below). Do not introduce a single rune into a legacy file.
6. Arabic follows the LOCKED conventions — MSA formal-neutral, no tashkeel in chrome, Western digits, Arabic punctuation, ICU plurals with all 6 categories, bidi-isolate mixed runs. → arabic-conventions.md (authoritative; apply without re-deciding).
7. Verify after every batch: npm run check + npm run build green, en/ar keys synced. Do NOT run npm run lint (pre-commit hook owns it; a manual pass fails on native-binding in fresh worktrees). → project-conventions.md §9.

The loop: extract → key → translate → verify

1. Extract — find the hardcoded chrome string (text node, or aria-label/title/placeholder/alt). Start at the seams where copy already lives centralized: lib/errors/friendly.ts, lib/sign-in-messages.ts, the *_LABELS enum→display maps. → project-conventions.md §7.
2. Key — invent area_component_purpose (snake_case, area-prefixed). Grep the whole messages/ tree for the id first — collisions are the silent last-wins bug. Add it to the area's en.json and ar.json in the same position.
3. Translate — author the ar value per arabic-conventions.md. Counts → ICU plural with all 6 Arabic categories. Mixed Arabic+Latin/number → bidi-isolate the foreign run.
4. Wire — replace the literal with m.<key>() using the correct per-mode pattern (below).
5. Verify — npm run check && npm run build green; en/ar key parity (diff of sorted keys).

Translate vs. don't-translate

Translate (UI chrome the app authored)	Do NOT translate (data the API owns)
Button / label / heading / tab / menu text	Reciter names (catalog data)
aria-label, title, placeholder, alt	Surah / chapter names → pick API name_ar / name_en by locale
Validation card titles + descriptions (at render site — see registry caveat)	Quran text, tokens, ayah glyphs, waveform shard letters
Error copy (friendly.ts), toasts, confirmations, sign-in prompts	Enum values sent to the backend (state/role/severity codes)
Keyboard-shortcut labels/descriptions (not the bindings)	Slugs, file paths, job IDs, SHAs, version tags, capability keys
Enum-derived pills/badges (the display string)	IDs, timestamps, bitrates, surah:ayah codes, units
Domain labels — "Surah", "Ayah 5", "Riwayah:" (key the label)	Product name ("Quranic Universal Audio", "Inspector"), brands (Hugging Face, GitHub, OAuth)

The nuance: ayah / surah / riwayah as a UI label is translatable chrome (key it); the entity value it points at is Arabic data (leave it). See arabic-conventions.md §5–6 for the full glossary + do-not-translate list.

Wiring patterns (Svelte5 runes vs legacy Svelte4)

Both rest on one fact: m.*() reads the ambient locale set by Paraglide's setLocale(). The per-mode question is only how the component re-renders when the locale flips. The single switch entry point is switchLocale() in src/lib/i18n/locale-store.ts (it updates the Paraglide ambient locale + the legacy store + the rune cell + <html dir/lang> together).

(a) Runes files — import * as m, call m.x() inline. Reactivity comes from reading the i18n rune (src/lib/i18n/locale.svelte.ts):

<script lang="ts">
  import * as m from '$lib/paraglide/messages';
  import { i18n } from '$lib/i18n/locale.svelte';
  // Reading i18n.locale makes this $derived re-run on switch.
  const heading = $derived((i18n.locale, m.dashboard_catalog_heading()));
</script>
<h1>{heading}</h1>
<input placeholder={m.dashboard_catalog_search_placeholder()} />

A top-level read of i18n.locale is enough to re-render the whole component; when in doubt gate a $derived on it.

(b) Legacy Svelte-4 files (e.g. App.svelte) — never add a rune. Subscribe to the localeStore mirror and reference $localeStore in a reactive block so Svelte-4 reactivity re-evaluates the message calls. The (dep, m.x()) comma-sequence is the load-bearing trick — it makes the statement depend on the store while still evaluating to the string (a tr<T>(dep, value) helper in locale-store.ts does the same):

<script lang="ts">
  import * as m from '$lib/paraglide/messages';
  import { localeStore } from '$lib/i18n/locale-store';
  $: lang = $localeStore;
  $: saveLabel = (lang, m.common_action_save());
</script>
<button on:click={onSave}>{saveLabel}</button>

If a legacy file is too tangled to thread $localeStore through every call, you have exactly two sanctioned options: migrate the file to runes first, or keep it legacy with the $localeStore idiom. Never a third.

Attributes take the function call directly: placeholder={m.x()}, aria-label={m.x()}, title={m.x()}, alt={m.x()}. In legacy files bind them to a reactive $: label = ($localeStore, m.x()) value or they go stale after a switch.

Interpolation & ICU plurals

Pass data through message params, never concatenation that splices chrome + data:

"dashboard_catalog_result_count": "Showing {shown} of {total} reciters"

{m.dashboard_catalog_result_count({ shown, total })}

Counts use ICU plural variants. English has 2 forms; Arabic has all 6 (zero, one, two, few, many, other) — author every one in ar.json or it falls through to other and reads wrong. FORBIDDEN: {n === 1 ? '' : 's'} and sentence-from-fragments concatenation. Full ICU shapes + Arabic category boundaries are in project-conventions.md §5 and arabic-conventions.md §10.

Bundle note: per-message deep imports

The compiler emits outputStructure: 'message-modules' — one module per message under src/lib/paraglide/messages/<key>.js. The barrel import * as m from '$lib/paraglide/messages' is the normal call style and tree-shakes. For a thin-slice seam that must stay lazy (e.g. sign-in-messages.ts backing object-keyed getters), deep-import the single message: $lib/paraglide/messages/common_signin_edit_title. Mind inlang issue #668 (barrel vs deep-import) — details in paraglide.md.

Reference subfiles

File	Read it when
paraglide.md	Library specifics — project.inlang location, array pathPattern, generated output dir, compile/build-order rule, the locale rune + setLocale(reload:false), switching locale in dev, deep-import vs barrel (#668), hand-author-only constraint.
arabic-conventions.md	Authoritative Arabic (MSA) chrome style — register, numerals, tashkeel, punctuation, the binding glossary, do-not-translate, interim bidi, gender/formality, ICU plurals, length/overflow. Apply verbatim.
project-conventions.md	Engineering contract — key naming/prefixes, file layout, hand-author rule, what to translate, per-mode wiring, interpolation/plurals, the seams, the registry parity caveat, deferred guides, verification commands.