Dapp i18n (ES/EN) with next-intl

[Cbiux]

Summary

Add i18n (ES/EN) to the dapp with next-intl — eliminate mixed Spanish/English copy across auth and dashboard.

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Background

Current UX mixes languages (e.g. Spanish errors in wallet-network.ts, English page titles). Landing is EN-first; LatAm users need consistent ES.

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Implementation

Library: next-intl (App Router)

Front/messages/en.json
Front/messages/es.json
Front/i18n/request.ts
Front/middleware.ts          # locale prefix or cookie

Scope (v1 pages):

• /, /login, /register
• /dashboard/*
• wallet-auth-card.tsx, api-errors.ts user-facing strings

Locale switcher: footer toggle in DappShell

Default: en; persist choice in cookie

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Acceptance criteria

• No hardcoded user-facing strings on scoped pages
• npm run build passes with both locales
• Locale switcher works without full page break
• CONTRIBUTING.md section: how to add translation keys
• API error messages stay English (server); map in api-errors.ts

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Out of scope

• Server-side i18n
• RTL languages