jimmysu0309/shinkansen — reverse-engineered prompt

Build me a fast, privacy focused browser extension called Shinkansen for Chrome, Firefox, and Safari that translates whole web pages and YouTube subtitles without sending browsing data through my own server. I want it to replace text in place so the page keeps its original layout and links still work, with a simple single language mode and a bilingual mode that shows the original plus the translation. It should support 8 target languages, let me use my own Gemini API key for the best quality, offer a free Google Translate option, and also allow a custom OpenAI compatible endpoint.

Please add a floating button, toolbar controls, keyboard shortcuts with 3 presets, auto translate for chosen sites, restore original text, page translation for Google Docs reading view, and real time YouTube subtitle translation with optional bilingual captions and smarter sentence grouping for auto captions. I also want local caching, basic cost and usage tracking, editable translations, a terminology glossary, blocked words, and a way to save translated articles to Instapaper. Look up current browser extension docs online if you need to.