Languages

Supported languages

yaku does not maintain a hardcoded language list. It passes the target language code to the LLM backend, which handles the actual translation. This means yaku supports every language that your chosen backend model can translate.

Common language codes (BCP 47 format):

Code	Language	Code	Language
en	English	ko	Korean
zh-TW	Traditional Chinese	th	Thai
zh-CN	Simplified Chinese	vi	Vietnamese
ja	Japanese	fr	French
de	German	es	Spanish
pt	Portuguese	it	Italian
ru	Russian	ar	Arabic

Use the full BCP 47 code when a language has regional variants. For example, zh-TW (Traditional Chinese as used in Taiwan) vs zh-CN (Simplified Chinese as used in Mainland China).

Language code validation

yaku validates --to and --from values against the BCP 47 standard. It normalizes case automatically (zh-tw → zh-TW) and rejects invalid codes with a helpful suggestion:

yaku --to japanese "Hello"
# Error: unknown language "japanese". Did you mean "ja"?

yaku --to zh-tw "Hello"
# Works — silently normalized to zh-TW

In the LLM prompt, yaku uses the display name alongside the code (e.g., “Translate to Japanese (ja)”) for clarity.

Target language (--to)

Every translation needs a target language. Specify it with --to:

yaku --to en "Bonjour le monde"
yaku --to en -f README.ja.md

Default target language

Set a default to skip --to on every command:

yaku config set default-target en

Now these are equivalent:

echo "Bonjour" | yaku --to en
echo "Bonjour" | yaku              # uses default-target

An explicit --to always overrides the default:

echo "Bonjour" | yaku --to es     # Spanish, not English

Source language (--from)

By default, yaku lets the LLM auto-detect the source language. This works well for most text:

yaku --to en "これはテストです"
# This is a test

Use --from when you need explicit control:

yaku --from ja --to en "これはテストです"

When to use --from:

• The text mixes multiple languages and auto-detection picks the wrong one.
• You need deterministic behavior in scripts or CI/CD pipelines.
• The text is very short (a few words) and the LLM guesses the wrong language.

Same-language hint

If --from and --to are the same language, yaku suggests using polish mode instead:

yaku --from en --to en "I want talk about the deploy issue"
# Hint: source and target language are both en. Consider using --mode polish for language refinement.

Translation quality tips

• Use the hosted backend — The default backend uses refined, per-language prompts that produce higher-quality translations. See Hosted Service & Plans for details.
• Add context — Use --context to hint the domain. This helps the LLM pick the right terminology:

  yaku --to en --context "medical documentation" -f report.zh-TW.md

• Use a glossary — For consistent terminology across a project, create a glossary file.
• Use polish mode for editing — If you already have a draft in the target language, --mode polish improves it without re-translating:

  yaku --mode polish --to en -f draft.md