opencode-translate

Use opencode in your native language. LLM always hears English.

Demo

Why

LLMs are worse in non-English. Benchmarks confirm it on every frontier model.

• Claude Opus 4.7 / GPT-5.5 / Gemini 3.1 Pro: identical coding tasks scored 5/5 in English but dropped to 0–1/5 in Arabic and Korean (LILT, 2025).
• Anthropic's own numbers: Japanese 96.9%, Korean 96.6%, Yoruba 80.3% — English is always the baseline (Anthropic docs).
• Token tax: Korean ~1.25×, Japanese ~1.25×, Arabic ~3× more tokens per equivalent content. Higher cost, smaller effective context.

This plugin lets you write in your language while the model works in English — best of both worlds.

Full research write-up: docs/why.en.md

Install

Version 2 of this plugin uses OpenCode's v2 public plugin API. The verified release is OpenCode 2.0.3. For OpenCode v1, use opencode-translate@1. Start a fresh v2 session when upgrading: v1 activation metadata and historical bilingual trailers are not migrated.

bun add -g opencode-translate

Setup

Add to ~/.config/opencode/opencode.jsonc:

{
  "$schema": "https://opencode.ai/config.json",
  "plugins": [
    {
      "package": "opencode-translate",
      "options": {
        "model": "openai/gpt-5.4-mini", // model to use for translation
        "variant": "minimal",          // optional model variant / thinking effort
        "lang": "Korean"               // language you speak
      }
    }
  ]
}

Quit and restart OpenCode after changing the plugin configuration. For a local build, run bun install && bun run build and set package to the absolute directory /path/to/opencode-translate/dist.

Usage

Prefix any message with $en to activate translation for that session.

$en 프로젝트 루트의 package.json을 읽고 요약해줘

All subsequent messages in the same session are translated automatically — no need to repeat $en.

• Your original message and its English translation remain visible in the transcript.
• Web composer presentation metadata is synchronized with the translated prompt, including failure notices; review-comment cards are preserved.
• The first successful $en prompt includes a Translation enabled: confirmation with the language and translator model.
• English assistant text streams normally; a translated Markdown section is appended when the text segment completes.
• Both the terminal and web UI display the same persisted bilingual assistant text. No UI-specific plugin is needed.
• Question forms are translated, with selected labels and custom answers converted back to English for the model.
• Translation activates only in root sessions. Its state survives plugin/server restarts.

Before model requests, the plugin removes its recorded display translations from context. It does not remove arbitrary Markdown based on its appearance. On inbound translation failure, the transcript shows Translation failed: and the error reason. The main model receives the original text without $en or the diagnostic; failed first-time activation remains inactive, so retry with $en after fixing the error. On outbound failure, the English response is retained with a translation-unavailable notice.

If $en has no effect

$en is a plugin control keyword, not an instruction for the main model. If the model comments on $en, inbound translation did not complete. In version 2.0.0, an inbound failure was only logged on the server and left $en in the prompt, making it indistinguishable from an unloaded plugin in the transcript.

Check the active server's plugin list and configuration, including the selected project location. It must load the v2 package, not an old pinned opencode-translate@1.x. Also check the configured translation model and variant; changing the main-chat model does not change the translator. An API-key login or OAuth connection must exist on that server. The server log message [opencode-translate] inbound translation failed contains the underlying generation error.

If replies translate but your own prompt still looks untranslated in the Web UI, inspect the stored user message's text and metadata.displayText. The Web UI prefers displayText, which versions up to 2.0.2 left at the original composer input even when text contained the English translation. The prompt hook now synchronizes that presentation field. This applies to newly admitted prompts; it does not rewrite presentation metadata on older messages.

For the Question tool, OpenCode can freeze the provider-owned question arrays. Versions up to 2.0.3 tried to mutate those arrays and fell back to English even after obtaining a valid translation. The before-tool hook now translates a copy and replaces event.input, preserving the original provider data. Already pending questions need a new tool invocation to pick up this fix.

OpenCode 2.0.3 also normalizes the legacy "plugin": [["package", { ...options }]] tuple syntax; that syntax alone does not prevent this plugin from loading. The plugins object form shown above is the recommended v2 format. Make sure the configuration is a complete JSON/JSONC object, including its opening {.

If there is neither an activation confirmation nor a failure notice, inspect the running server's plugin state for the same directory as the session:

opencode api v2.plugin.awaitActivation --param 'location[directory]=/absolute/path/to/project'
opencode api v2.plugin.list --param 'location[directory]=/absolute/path/to/project'

Find opencode-translate, check source.version and state.status, and inspect state.error if setup failed. If the UI uses a remote or explicitly selected server, pass --server with that same server URL. A client version or a globally installed npm version alone does not establish what the session's server has loaded.

Authentication

Connect the translation model's provider in OpenCode itself. Translation uses the public ctx.generate.text() API, with a ctx.session.generate() fallback for providers that require an OpenCode session. OpenCode owns provider selection, model variants, API keys, SQLite credentials, and OAuth refresh/persistence. The plugin does not read auth.json/auth-v2.json, query the credential database, or maintain separate tokens. Provider and OAuth support for the translation model is the support available in your OpenCode installation.

Verified on OpenCode 2.0.3 using the host's saved credentials:

Translation model	Result
openai/gpt-5.6-luna	Inbound, outbound, and follow-up translation passed through stateless generation with ChatGPT OAuth.
opencode/muse-spark-1.3-contributor-free	Passed through the session-aware fallback described below.
opencode-go/gpt-5.6-luna	Passed through the same session-aware fallback (Go's x-opencode-session rejection, not Zen's free-tier one).
anthropic/claude-sonnet-5 with @henadev/opencode-anthropic-auth@0.2.0	Works as the main chat model, but not as the translator in this release: its auth plugin depends on session HTTP hooks that stateless generation skips.

Anthropic translation succeeded in a session-aware experiment, but the automatic fallback in this release is limited to the explicit OpenCode session-metadata rejections described below. It does not retry generic authentication errors through another path.

OpenCode session-metadata-only translation models

ctx.generate.text() omits the session request metadata every Console tier requires (Zen opencode and Go opencode-go, and presumably any tier Console adds later). The plugin recognizes this upfront, from the configured provider ID -- isSessionOnlyProvider() -- and routes those providers straight to session-aware generation without ever attempting the stateless call. This is deliberate: Console has phrased the rejection differently by tier and release (the free Zen tier: OpenCode's free tier can only be used in/from within OpenCode.; the paid Go tier: Request is missing x-opencode-session and cannot be routed efficiently.), and a provider-ID check that's known before the request is sent can't be broken by wording changes on Console's side -- unlike matching the rejection message, which has already needed two updates.

Matching the rejection message (isSessionMetadataRequired()) still exists as a safety net for providers isSessionOnlyProvider() doesn't recognize: on that specific rejection, mid-translation, the plugin switches the same way. Both paths converge on public session-aware generation using a reusable Translation helper session for the configured model and location. The helper may appear in the session list. Translation prompts are transient: they do not append messages to either the helper or your chat, and each generation receives only the current translation prompt plus OpenCode's system instructions and tool definitions. The helper ID survives plugin/server restarts. Other authentication or model-selection failures still report their original error.

This was verified with opencode/muse-spark-1.3-contributor-free (Zen) and opencode-go/gpt-5.6-luna (Go): normal session generation succeeds on both, ctx.generate.text() lacks the session request metadata either provider accepts, and with the provider ID recognized upfront, the plugin never attempts the stateless call in the first place for either one.

Tool definitions are deliberately kept in the helper session's requests. Console's free tier reads a request with an emptied tool list as non-agent traffic and rejects it with the same free tier can only be used within OpenCode error, even when the request otherwise carries correct session headers -- confirmed by comparing requests with and without tool definitions against the real opencode.ai/zen backend. This is harmless for translation: the plugin's session-generate call never runs a tool loop, so the model cannot actually execute anything even though it can see the schemas.

Inline reply support

V2 has no experimental.text.complete hook or public display-only message append operation. Inline translations use session.hook("http.response", ...) with adapters for these main-chat response protocols:

Protocol	Recognized endpoint	Support
OpenAI Responses, including Codex	…/responses	SSE text deltas and final snapshots
OpenAI Chat Completions and compatible providers	…/chat/completions	SSE text choices
Anthropic Messages	…/messages	SSE text blocks
Gemini / Vertex Gemini	…:streamGenerateContent	SSE non-thinking text

Unknown endpoints, non-SSE responses, and binary protocols such as Bedrock Converse pass through unchanged with a server log message. They still support inbound/question translation when the translation model is available through OpenCode. Reasoning, tool calls, images, and other non-text outputs are not translated.

Transport: OpenCode routes sessions through HTTP when HTTP hooks are registered. Loading this plugin therefore disables the session WebSocket fast path in its location, including sessions that have not activated $en. Translations add latency at text-completion boundaries and use additional model requests. Their usage is separate from the primary model's reported token counts.

Development and verification

bun install
bun run check:ci
bun run typecheck
bun run knip
bun test
bun run build
bun run test:package

# Requires Node 24 and an OpenCode v2 binary; uses an isolated server and fake provider.
OPENCODE_BINARY=/path/to/opencode bun run test:host

# Exercise a registry-installed package through OpenCode's actual package loader.
OPENCODE_BINARY=/path/to/opencode OPENCODE_TRANSLATE_PACKAGE=opencode-translate@latest bun run test:host

# Verify OpenCode's normalization of legacy plugin tuples as well.
OPENCODE_BINARY=/path/to/opencode OPENCODE_TRANSLATE_LEGACY_CONFIG=1 bun run test:host

# Verify providers that support ordinary stateless generation.
OPENCODE_BINARY=/path/to/opencode OPENCODE_TRANSLATE_REQUIRE_SESSION=0 bun run test:host

Tests include OpenCode's actual native protocol parsers. The real-host smoke test loads the built plugin, creates and rotates a test credential in an isolated SQLite database, checks bilingual persisted messages and English-only model requests, and restarts the server to verify recovery. It does not use your live server, credentials, or paid models. It also executes the real Question tool, checks translated form fields, submits selected options and a Korean custom answer, and verifies that the next model request contains the original English questions and English answers. CI covers both configuration formats and both generation paths. The publish workflow tests the candidate before publishing, then installs the exact version from npm in OpenCode before creating its GitHub release.

The old opencode2 v0.0.0-dev-18322 binary does not pass this migration's host smoke test. Use the verified 2.0.3 release rather than assuming that any binary named opencode2 exposes the current plugin API.

Options

Option	Type	Default	Description
model	string	required	Translator model in provider/model-id form
variant	string	optional	Translator model variant / thinking effort (for example, "minimal", "high", or "max")
lang	string	required	Language you speak (e.g. "Korean", "Japanese")
trigger	string[]	["$en"]	Keywords that activate translation
verbose	boolean	false	Print translation logs