## Why
### Problem
The app had two categories of localization gaps:
1. Many UI strings were not translated — Spanish users saw raw English
text because keys were missing from `lang/es.json`.
2. All currency and number formatting was hardcoded to `'en-US'` (or
`undefined`), so amounts always formatted in English style regardless of
the user's locale setting.
## What
### Changes
- **`lang/es.json`** — Added 22 missing Spanish translation keys
covering onboarding, automation rules, balance history, dashboard, and
more.
- **`utils/currency.ts`** — Added `locale` parameter (default `'en-US'`)
to `formatCurrency`.
- **`utils/chart.tsx`** — Added `locale` parameter to
`formatCurrencyWithCode`; replaced `.toLocaleString()` calls with
locale-aware versions.
- **`hooks/use-dashboard-data.ts`** — Added `locale` param to
`formatMonth` and `deriveAccountMetrics`; wired `useLocale()` inside
`useDashboardData`.
- **`pages/dashboard.tsx`** — Added `useLocale()` and passed `locale` to
`deriveAccountMetrics`.
- **`components/charts/sankey-chart.tsx`** — Added `locale` param to
`formatAmount` and threaded it through `OtherCategoriesBreakdown`.
- **`components/charts/mom-chart.tsx`** — Replaced hardcoded `'en-US'`
in YAxis tickFormatter with `useLocale()`.
- **`components/budgets/budget-list-card.tsx`** — Passed `locale` to all
`formatCurrency` calls.
- **`components/budgets/budget-spending-chart.tsx`** — Passed `locale`
to all `formatCurrency` calls in `CustomTooltip`.
- **`components/ui/amount-display.tsx`** — Added `useLocale()` and
passed to `Intl.NumberFormat`.
- **`components/ui/amount-input.tsx`** — Added `useLocale()` and passed
to `Intl.NumberFormat` used for display formatting.
- **`components/accounts/balances-modal.tsx`** — Added `useLocale()` for
both the balance formatter and `formatDate`.
- **`components/transactions/edit-transaction-dialog.tsx`** — Replaced
hardcoded `'en-US'` with `useLocale()`.
-
**`components/accounts/import-balances/import-balance-step-mapping.tsx`**
— Replaced `'en-US'` with `useLocale()` in preview formatting.
- **`components/transactions/import-step-mapping.tsx`** — Replaced
`'en-US'` with `useLocale()` in preview formatting.
- **`components/onboarding/step-create-account.tsx`** — Fixed garbled
Spanish caused by 3-part JSX string concatenation; replaced with single
translation key.
- **`components/automation-rules/create-automation-rule-dialog.tsx`** —
Fixed multiline description key mismatch with `es.json`.
## Verification
### Tests
- TypeScript check (`npx tsc --noEmit`) passes with no new errors
introduced by these changes.
- `lang/es.json` validated as well-formed JSON.
### Manual
- With locale set to `es`, all previously untranslated strings now
render in Spanish.
- Currency amounts format according to the user's locale (e.g.,
`1.234,56 €` in `es` vs `$1,234.56` in `en-US`).
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