Shinkansen - Blazing fast web & YouTube translator by Jimmy Su

Shinkansen is a fast, private, high-quality translation extension that uses AI models to translate foreign-language web pages, YouTube subtitles and documents into your language. Text is replaced in place so the page layout stays intact, and requests go straight to the AI model — your data never passes through a third party

Recent major updates:

• Added Word (.docx) document translation — the translation is written back into the original file with layout, styles, tables, images and comments preserved; monolingual or bilingual output
• Added subtitle file translation (SRT, WebVTT, ASS) — timing and style tags are preserved; download bilingual subtitles
• PDF translation: limits raised to 50 MB and 300 pages with a selectable page range; fixed two-column short lines, colored backgrounds, rotated pages, overflowing paragraphs and more
• Cheaper web translation — batches are twice as large, so each page needs half the API requests and about a third fewer input tokens, at the same speed
• Respects the page's do-not-translate markup — names, codes and code that site authors mark as not-to-translate stay untouched and are never sent to the API; icon-font glyphs are no longer turned into text
• Automatic Simplified ↔ Traditional Chinese conversion is on by default — pages in the opposite variant convert locally on load, free and without API calls; turn it off in the toolbar icon menu
• YouTube subtitles — auto-caption AI segmentation costs about half as much; timing fixes, earlier display, no stale captions when switching videos
• iOS and iPadOS version is on the App Store — a Safari extension with four-finger touch translate and the floating button

Features:

Instant translation
The page starts changing within 1 second of pressing translate — no waiting for the whole batch of API calls to come back first (Gemini only)

Preserves page layout
In-place text replacement keeps fonts, sizes, colors and links intact — it looks like a page originally written in your language

Bilingual side-by-side
Original and translation shown together for language learning or proofreading; switch between overlay and bilingual modes anytime

Multi-language translation + UI
Translate into any of 8 target languages, and the extension interface switches to match

Document translation
Upload a whole PDF, EPUB book, Word document, TXT, Markdown, HTML or subtitle file — everything is processed inside the browser, nothing is uploaded to a server. PDF output keeps the original layout; EPUB gets a book-wide glossary and a post-translation consistency scan; Word translations are written back into the original file; edit any paragraph before exporting, with monolingual or bilingual output for most formats

YouTube subtitle translation
Watch YouTube videos with the captions auto-translated into your language, with optional bilingual display; auto-generated captions are re-segmented by meaning into readable full sentences

Respects do-not-translate markup
Content that site authors mark as not-to-translate is kept as-is and never sent to the API, and icon-font glyphs are never turned into text

Auto-translate across pages
Once a page is translated, clicking links or pressing Back also auto-translates the next page — no need to trigger translation on every page

Floating button
A draggable button at the page edge: tap to translate, long-press to switch engines or open the menu; position, size and opacity are adjustable

Custom glossary
Pin specific terms to your preferred translations so proper nouns are always rendered consistently — global and per-site layers, CSV import, room for hundreds of entries

Blocked-word list
An editable list of words you don't want in the translation (26 defaults). Block a word on its own, or pair it with a required replacement — the LLM is explicitly instructed to comply

Translate opening only
Preview the first few paragraphs before deciding whether to translate the whole article — saves a lot of tokens

Translation cache
Already-translated paragraphs are cached automatically — re-opening the same page costs nothing

Transparent pricing
Cost is shown live during translation. The settings page tracks token usage and cost for every past run, with charts and CSV export

Three translation engines
Gemini, Google Translate and custom models coexist as three engines — switch freely depending on context. A custom model can point at any OpenAI-compatible endpoint, whether a cloud service or a model you run yourself

Free Chinese variant conversion
Built-in dictionaries convert between Simplified and Traditional Chinese locally — no API key, no API calls, works offline — with phrase-level Taiwan-convention mapping. Auto-convert on page load is on by default

Send to Instapaper
Save the whole translated article to Instapaper in one click, with a summary in your target language, for later re-reading

Custom shortcuts
Three customizable shortcuts (Alt+A, Alt+S, Alt+D) for switching engines and models on the fly