How to Use Linguistic Instructions for AI Translation

Linguistic instructions let you write plain-language guidance that is passed to the AI before every translation. They give you fine-grained control over style, tone, formality, and domain-specific behaviour — beyond what a glossary alone can achieve.

1. Create an instruction: Click New Instruction, give it an optional name, then select the source language (e.g., en-US) and target language (e.g., de-DE).
2. Write the instruction text: Describe in natural language how the AI should translate. For example: "Use formal language. Do not use contractions."
3. Activate the instruction: Toggle Active to apply it automatically to every translation for the selected language pair. Only one instruction per language pair can be active at a time.
4. Translate with guidance: Run your translation as usual. The active instruction is injected into the AI prompt automatically — no extra steps are needed.
5. Edit or update instructions: Click the edit button on any instruction to update its name, text, or active status directly in the list. No page navigation required.

What Are Linguistic Instructions?

Linguistic instructions are free-text directives that guide the AI translation engine's behaviour for a specific source-to-target language pair. Unlike a glossary — which enforces specific term mappings — instructions provide stylistic and structural guidance that shapes how all text is translated.

For example, an instruction might say: "Translate in a formal register. Use the Sie form in German. Avoid technical jargon unless the source text explicitly uses it. Never translate product names." This guidance is applied globally to every string in the translation request.

Instructions are particularly powerful for teams with a defined brand voice, legal requirements around language register, or audience-specific communication styles that must be maintained consistently across all translated content.

How Linguistic Instructions Work

When you trigger a translation, l10n.dev checks whether an active instruction exists for the current source-to-target language pair. If found, the instruction text is prepended to the AI prompt as a system-level directive, ensuring the model follows your guidance for every string in the request.

Instructions work alongside glossaries. If both are active for the same language pair, both are applied simultaneously — the instruction shapes the overall style while the glossary enforces specific term choices. This combination gives you maximum control over translation quality.

Linguistic Instructions vs. Glossaries

Glossaries and linguistic instructions serve complementary but distinct purposes. A glossary is a term-level constraint: it maps specific source words to approved target words and ensures the AI always uses those exact terms. An instruction is a style-level directive: it describes the desired register, tone, grammar rules, and general behaviour.

Use a glossary when you need to lock in translations for specific terms (e.g., product names, legal phrases, UI labels). Use a linguistic instruction when you want to define how the AI writes overall — formality, sentence structure, avoidance of certain constructions, or domain-specific conventions.

Common Use Cases for Linguistic Instructions

Linguistic instructions are effective wherever translation quality depends on more than just word choice:

• Tone and register control: Enforce formal or informal registers for different markets — for example, always use Sie (formal) in German consumer communications.
• Audience-specific formality: Adjust the level of formality based on the target audience — casual for a gaming app, professional for a financial services platform.
• Domain-specific conventions: Instruct the AI to apply legal, medical, or technical writing conventions appropriate for highly regulated industries.
• Brand voice consistency: Encode your brand voice guidelines directly — e.g., concise sentences, active voice, no passive constructions, no hyperbole.
• Regional and cultural adaptation: Provide cultural notes to help the AI avoid expressions that may not resonate with the target audience.

Tips for Writing Effective Instructions

Well-written instructions produce noticeably better translation results. Here are some best practices:

• Be specific and actionable: Instead of "be professional", write "use formal register, avoid contractions, and address the reader as Sie in German". Concrete rules are easier for the AI to follow.
• Include examples where helpful: For complex style rules, a short example can clarify intent — e.g., "Translate 'Sign up' as 'Jetzt registrieren', not 'Anmelden'".
• Keep instructions focused: Aim for a few clear, well-phrased rules rather than an exhaustive list. Overly long instructions may dilute the impact of individual rules.
• Combine with a glossary: Use instructions for style and tone; use a glossary for specific term mappings. Together they give you comprehensive control over translation output.

Frequently Asked Questions

How many instructions can I create?

You can create up to 5 instructions per source-to-target language pair. Only one instruction can be active per language pair at a time.

What happens if I activate a second instruction for the same language pair?

The previously active instruction for that language pair is automatically deactivated. Only one instruction per language pair can be active at any time.

What should I write in the instruction text?

Write plain-language guidance describing how the AI should translate. Examples: "Use formal register." "Do not translate product names or brand names." "Preserve all HTML tags exactly as written." "Use the active voice wherever possible."

Does an instruction apply to all language pairs?

No. Each instruction is scoped to a single source language and a single target language. You can create separate instructions for different translation directions — for example, one for English → French and another for English → German.

Can I use an instruction and a glossary at the same time?

Yes. If both an active instruction and an active glossary exist for the same language pair, both are applied simultaneously during translation. The instruction guides the overall style while the glossary enforces specific term choices.