Selection translation
Translate any highlighted text
Highlight text on any page. Swiftin shows a small floating "S" button near your cursor, then a popup with the translation when you click it. The popup also holds an engine picker, language selectors, TTS, and copy buttons — everything on one card.
How a selection translation runs
Two-stage on purpose — selecting text doesn't fire a request, only your click does. Keeps the page quiet when you're reading.
- 1Highlight text with the mouse — `selectionchange` + `mouseup` events fire
- 2A floating "S" button appears near the end of your selection
- 3Click the button — the popup opens in a loading state and the translate request fires
- 4The translation renders inline; engine, language, TTS and copy controls are right there
What's in the popup
One card with everything. No extra menus, no settings page round-trip.
Engine switcher
Switch engine right inside the popup — Google, Bing or any AI brand. The choice persists as your selection engine for next time.
Language selectors
Source language defaults to Auto (server-detected; client-side trigram fallback if the server didn't return one). Target language is searchable.
Speaker icons (×2)
Two speaker buttons — one for the translation, one for the source. See Text-to-Speech for engine and quota details.
Copy + pin
Copy the original or the translation to clipboard. Pin keeps the popup open while you click around the page.
Engine for selection vs page / input
Each surface has its own engine setting. `settings.selectionTranslationEngine` lives independently from page and input. Switching the engine in the popup updates this key — the next selection on a fresh page uses your last choice.
Free plans get Google and Bing for selection. Pro/Team pick any AI brand; BYOK users can plug their own key per brand (see BYOK docs).
Listening to the translation
The popup has a speaker icon next to the translation and another next to the original. Pro/Team accounts get AI voice (Gemini TTS, Kore/Orus voice); Free accounts use the browser's built-in voice for the user's OS. AI-quota exhausted = silent fallback to browser voice. Text-to-Speech →
Where it works (and where it doesn't)
Selection sits on the browser's native Selection API — works wherever the browser hands us text.
Plain HTML pages
Articles, blogs, social feeds, docs — anywhere browser's `window.getSelection()` returns text.
Shadow DOM
The SelectionPopup itself mounts in a closed Shadow DOM (no host-page CSS leaks). Selection inside other Shadow DOMs is captured via `composedPath`.
PDFs & canvas
PDF viewer uses a special rendering surface — selection works only if the viewer exposes text via the DOM. Canvas is bitmap, so no text to select.
Excluded sites
Global excludes (`excludedSites`), selection-only excludes (`selectionExcludedUrls`), and per-host overrides (`siteOverrides[host].selectionDisabled`) each disable the popup. Configure them in Options → Excluded URLs.
Saving selection translations
Off by default. Two switches must both be on: the master `Save translation history` and the per-source `Save selection translation history`. Free plans keep history local-only; Pro/Team can opt in to cloud sync separately. See the History docs. History →
Common issues
If the popup misbehaves on a specific page, check the table below — most cases fix themselves in a click or two.
NO_POPUPPopup doesn't appear
Extension globally disabled, the site is in your excluded list, or you snoozed selection translation. Check Options → General toggle, Excluded URLs, and per-host overrides.
PDF_VIEWERSelection on PDF does nothing
Some PDF viewers expose text to the DOM, some don't. If your viewer doesn't, selection translation can't see the text. Open the PDF in a text-exposing viewer or copy-paste into the input translator.
CANVASText in a canvas / image is ignored
Canvas text is a bitmap — there is no DOM text to select. No fix at the extension level; the site would have to expose text as DOM.
WRONG_LANGAuto-detect picks the wrong source language
Short or mixed text trips the trigram detector. Open the source-language dropdown in the popup and set it explicitly.
SAME_LANG"Already in your target language" message
Auto-detected source equals your target. If detection is wrong, override the source in the popup; otherwise the translation would be a no-op.
ENGINE_FAILEDEngine error badge in popup
Provider rejected the request (quota, auth, rate-limit). Switch engine inside the popup; for BYOK, see the BYOK error table for the exact code.
NO_AI_VOICESpeaker icon plays a poor-quality voice
AI voice quota exhausted or you're on Free — extension falls back to your OS voice. Quality varies by OS. Upgrade or install a better system voice for that language.