Declarative Agent Developer

Localization Workflow

Quick Reference — Complete Localization Checklist

For adding localization to an agent (Workflow A):

1. ⛔ Tokenize declarativeAgent.json → replace name, description, all conversation_starters[].title and .text with [[token]] syntax

2. ⛔ Create language files → en.json (default) + one per additional language, each with name.short, name.full, description.short, description.full, and localizationKeys mapping EVERY token

3. ⛔ Update manifest.json → add localizationInfo with defaultLanguageTag, defaultLanguageFile, additionalLanguages

4. ⛔ Deploy → npx -y --package @microsoft/m365agentstoolkit-cli atk provision --env local --interactive false

For adding a language to an already-localized agent (Workflow B):

1. Read existing default language file to get the list of localizationKeys

2. Create new {lang}.json with the SAME set of keys, translated values

3. Add new entry to additionalLanguages in manifest.json

4. ⛔ Deploy

This document provides step-by-step instructions for localizing an M365 Copilot declarative agent into multiple languages.

Localization spans two layers: the app manifest (manifest.json) and the declarative agent manifest (declarativeAgent.json). Both use the same set of language files, but reference strings differently.

Important: If an agent supports more than one language, you must provide a separate language file for every supported language, including the default language. Single-language agents do not require language files.

⛔ STOP — READ THIS FIRST

Two Localization Scenarios

⛔ MANDATORY: You MUST check which scenario applies BEFORE making any changes. Read manifest.json to see if localizationInfo exists, and read declarativeAgent.json to see if it already uses [[token]] syntax.

⛔ Anti-Patterns — NEVER Do These

How Localization Works

Both types of localized strings live in the same language file per locale.

Workflow A: Add Localization to an Agent

Use this workflow when localizing an agent for the first time — the agent currently has hardcoded strings and no localizationInfo.

Step A1: Tokenize Agent Manifests — MANDATORY

Replace ALL user-facing strings in declarativeAgent.json (and plugin.json, if applicable) with tokenized keys wrapped in double brackets ([[key_name]]).

You MUST tokenize ALL of these fields:

Token key rules:

• Must match the pattern: ^[a-zA-Z_][a-zA-Z0-9_]*$

• Use descriptive, snake_case names (e.g., starter_vpn_title not key1)

• Keep names consistent across agent and plugin manifests

Example — tokenized declarativeAgent.json:

{
  "$schema": "https://developer.microsoft.com/json-schemas/copilot/declarative-agent/v1.6/schema.json",
  "version": "v1.6",
  "name": "[[agent_name]]",
  "description": "[[agent_description]]",
  "instructions": "$[file]('instructions.txt')",
  "conversation_starters": [
    {
      "title": "[[starter_vpn_title]]",
      "text": "[[starter_vpn_text]]"
    },
    {
      "title": "[[starter_password_title]]",
      "text": "[[starter_password_text]]"
    }
  ],
  "disclaimer": {
    "text": "[[disclaimer_text]]"
  }
}

If API plugin exists — tokenize plugin.json too:

{
  "schema_version": "v2.4",
  "name_for_human": "[[plugin_name]]",
  "description_for_human": "[[plugin_description]]",
  "description_for_model": "[[plugin_model_description]]"
}

⛔ NEVER skip tokenization. Writing localization files without first tokenizing the manifests makes localization non-functional. The manifests MUST use [[token]] syntax for the language files to take effect.

✅ POST-TOKENIZATION CHECKPOINT — Verify before proceeding to Step A2:

• [ ] name field uses [[agent_name]] or similar token

• [ ] description field uses [[agent_description]] or similar token

• [ ] Every conversation_starters[].title uses a [[token]]

• [ ] Every conversation_starters[].text uses a [[token]]

• [ ] instructions field is NOT tokenized (it should remain as $[file]('instructions.txt') or inline text — never [[token]])

If any box is unchecked, STOP and fix it before continuing.

Step A2: Create Language Files — MANDATORY

Create one JSON file per language in appPackage/, named {languageTag}.json (e.g., en.json, fr.json, ja.json).

Every language file MUST contain:

1. $schema — The localization schema reference

2. App manifest strings — name.short, name.full, description.short, description.full (all four are REQUIRED)

3. localizationKeys object — One entry per [[token]] used in declarativeAgent.json and plugin.json, using the token name WITHOUT brackets

Default language file (en.json) — use the ORIGINAL English values from the agent:

{
  "$schema": "https://developer.microsoft.com/json-schemas/teams/vDevPreview/MicrosoftTeams.Localization.schema.json",
  "name.short": "IT Help Desk",
  "name.full": "IT Help Desk Agent",
  "description.short": "Resolve common IT issues",
  "description.full": "Helps employees resolve common IT issues using internal knowledge bases and ticketing systems.",
  "localizationKeys": {
    "agent_name": "IT Help Desk Agent",
    "agent_description": "Helps employees resolve common IT issues using internal knowledge bases and ticketing systems.",
    "starter_vpn_title": "VPN issues",
    "starter_vpn_text": "I can't connect to the corporate VPN. What should I try?",
    "starter_password_title": "Password reset",
    "starter_password_text": "How do I reset my password?",
    "disclaimer_text": "This agent provides general IT guidance. For urgent issues, contact the helpdesk directly."
  }
}

Additional language file (fr.json) — use translations provided by the user:

{
  "$schema": "https://developer.microsoft.com/json-schemas/teams/vDevPreview/MicrosoftTeams.Localization.schema.json",
  "name.short": "Support informatique",
  "name.full": "Agent de support informatique",
  "description.short": "Résoudre les problèmes informatiques courants",
  "description.full": "Aide les employés à résoudre les problèmes informatiques courants à l'aide des bases de connaissances internes.",
  "localizationKeys": {
    "agent_name": "Agent de support informatique",
    "agent_description": "Aide les employés à résoudre les problèmes informatiques courants à l'aide des bases de connaissances internes.",
    "starter_vpn_title": "Problèmes de VPN",
    "starter_vpn_text": "Je n'arrive pas à me connecter au VPN de l'entreprise. Que dois-je essayer ?",
    "starter_password_title": "Réinitialisation du mot de passe",
    "starter_password_text": "Comment réinitialiser mon mot de passe ?",
    "disclaimer_text": "Cet agent fournit des conseils informatiques généraux. Pour les problèmes urgents, contactez le service d'assistance directement."
  }
}

⛔ CRITICAL: The localizationKeys in EVERY language file must have the EXACT SAME set of keys. If en.json has agent_name, agent_description, starter_vpn_title, etc., then fr.json must also have ALL of those same keys. Missing keys cause runtime resolution failures.

If the user did not provide translations for some strings (e.g., conversation starters), you MUST ask the user for them. Do NOT invent translations.

Step A3: Add localizationInfo to manifest.json — MANDATORY

Add the localizationInfo section to manifest.json:

{
  "localizationInfo": {
    "defaultLanguageTag": "en",
    "defaultLanguageFile": "en.json",
    "additionalLanguages": [
      {
        "languageTag": "fr",
        "file": "fr.json"
      },
      {
        "languageTag": "es",
        "file": "es.json"
      }
    ]
  }
}

Rules:

• defaultLanguageTag and defaultLanguageFile are always required

• Each additional language needs an entry in additionalLanguages

• Language files live in appPackage/ alongside the manifests

• Use language-only tags (e.g., en rather than en-us) for top-level translations; add region-specific overrides only when needed

Step A4: Deploy — MANDATORY

After completing ALL localization changes, deploy the agent:

npx -y --package @microsoft/m365agentstoolkit-cli atk provision --env local --interactive false

Then read M365_TITLE_ID from env/.env.local and present the test link. ⛔ Never skip deployment after localization changes.

Workflow B: Add a Language to an Already-Localized Agent

Use this workflow when the agent is ALREADY localized (manifests use [[tokens]], localizationInfo exists, language files exist) and the user wants to add another language.

⛔ Do NOT re-tokenize manifests or recreate existing language files. Only create the NEW language file and update localizationInfo.

Step B1: Read Existing Localization Setup

1. Read manifest.json — note the localizationInfo section (default language, existing additional languages)

2. Read the default language file (e.g., en.json) — note ALL keys in localizationKeys (these are the keys the new file must also have)

3. Read declarativeAgent.json — confirm it uses [[token]] syntax (if not, switch to Workflow A)

Step B2: Create the New Language File

Create appPackage/{languageTag}.json with:

1. $schema — same as existing language files

2. name.short, name.full, description.short, description.full — translated values from the user

3. localizationKeys — one entry per key from the default language file, with translated values from the user

⛔ CRITICAL: The new file MUST have the EXACT SAME set of localizationKeys as the default language file. Copy the key names from the existing default language file and fill in translated values.

Step B3: Update localizationInfo in manifest.json

Add the new language to the additionalLanguages array:

{
  "languageTag": "pt-BR",
  "file": "pt-BR.json"
}

⛔ Do NOT modify existing language files or the defaultLanguageFile entry. Only add to additionalLanguages.

Step B4: Deploy — MANDATORY

Deploy the agent:

npx -y --package @microsoft/m365agentstoolkit-cli atk provision --env local --interactive false

Then present the test link. ⛔ Never skip deployment.

Localizable Fields Reference

Declarative agent manifest:

API plugin manifest:

Required App Manifest Keys in Every Language File

Language Resolution Order

The Microsoft 365 host resolves strings in the following order:

1. Start with the default language strings

2. Overwrite with the user's language-only file (e.g., en)

3. Overwrite with the user's language + region file (e.g., en-gb), if available

For example, if the default language is fr, and you provide en and en-gb files, a user with locale en-gb sees: fr → overwritten by en → overwritten by en-gb.

Tip: Provide top-level, language-only translations (e.g., en rather than en-us). Add region-specific overrides only for the few strings that need them.

Project Structure

A localized app package includes the language files alongside the manifests:

my-agent/
├── appPackage/
│   ├── manifest.json
│   ├── declarativeAgent.json
│   ├── instructions.txt            # externalized instructions (NOT tokenized)
│   ├── plugin.json                 # optional
│   ├── en.json                     # default language file
│   ├── fr.json                     # French language file
│   ├── es.json                     # Spanish language file
│   ├── color.png
│   └── outline.png
├── env/
│   └── .env.dev
└── m365agents.yml

Critical Rules

1. Every [[token]] must have a matching localizationKeys entry in every language file. Missing keys cause runtime failures.

2. Keep token names descriptive — use starter_vpn_title not key1.

3. Do NOT localize instructions — externalize to instructions.txt via $[file]('instructions.txt'). Never use [[tokens]] for instructions.

4. Schema version consistency — $schema in language files must match manifest.json.

5. Always deploy after localization changes.

6. Do NOT invent translations — ask the user for translated strings. Never machine-translate without confirmation.

7. Tokenization is MANDATORY — language files have no effect without [[token]] syntax in the manifests.

⛔ FINAL GATE — Before Responding to the User

STOP. Before writing your response, verify ALL of the following:

• [ ] declarativeAgent.json uses [[token]] syntax for ALL localizable fields (name, description, every conversation starter title/text, disclaimer)

• [ ] instructions field is NOT tokenized (never use [[token]] for instructions)

• [ ] A default language file exists (e.g., en.json) with name.short, name.full, description.short, description.full, and ALL localizationKeys

• [ ] Every additional language file has the EXACT SAME set of localizationKeys as the default

• [ ] manifest.json has localizationInfo with defaultLanguageTag, defaultLanguageFile, and additionalLanguages

• [ ] I deployed with npx -y --package @microsoft/m365agentstoolkit-cli atk provision --env local --interactive false

• [ ] I presented the test link

If you cannot check ALL boxes, you are NOT done. Go back and complete the missing steps.

Error Handling

Learn More

• Localize your agent — Official Microsoft localization guide for agents

• Localize your app (Microsoft Teams) — General Teams app localization reference

• Localization schema reference — JSON schema for localization files