Feature: Translate notes to user's preferred language #1055

Feature Request: Translate Notes to User's Preferred Language

Summary

Add the ability to translate notes (kind 1 posts) into the user's preferred language, similar to the translation feature on X/Twitter and what Damus and Amethyst already offer.

Motivation

Nostr is a global protocol, but language barriers make it hard to follow conversations outside your native language. For example, following WNBA content on Nostr means missing out on posts from international fans who write in Spanish, French, Portuguese, and other languages. Right now the only option is to manually copy-paste into an external translation service.

Proposed Approaches

1. User-provided API key — User selects a translation provider (Google Translate, DeepL, LibreTranslate) and supplies their own API key. No cost to Primal.
2. Backend-integrated (Premium feature) — Primal handles translation server-side, caching results to minimize API costs. Could be a Premium tier feature. No user setup required.
3. Self-hosted LibreTranslate — Allow users to point at a custom LibreTranslate instance URL (great for self-hosters).

Cross-references

• Web app request (open since May 2025): Translate post to user language primal-web-app#133
• iOS app request: Feature: Translate notes to user's preferred language primal-ios-app#206
• Amethyst already has note translation built in
• Damus also supports note translation

Desired UX

• A "Translate" button on individual notes in a foreign language
• Optionally: a feed-level toggle to auto-translate all notes to the user's language
• Language preference set in Settings

Context

The web client already has an open feature request (#133) with 10+ upvotes and active technical discussion. Filing this here so the mobile apps track the same feature in parallel.