extraction agent failed to resolve locale aliases in next.config error

Fix the extraction agent failing to resolve locale aliases in next.config

TL;DR

The agent reads locales from one place but your aliases live in next.config, so teach it to read the config. Locale aliases like mapping en to en-US are config, not convention, and the agent guessed wrong. Point the agent at the next.config i18n block and resolve aliases from there.

The error

Extraction agent: failed to resolve locale alias "en"
next.config.js maps locales: ["en-US", "en-GB"], defaultLocale: "en-US"

Fix it

Step 1: Show the agent the real config

grep -n -A 8 "i18n" next.config.js | head -12

Expected: You see the locales list and defaultLocale the agent must use.

Step 2: Configure the agent to read next.config

node -e "console.log('set the agent locale source to next.config.js i18n.locales instead of its default guess')"

Expected: The agent reads the authoritative list.

Step 3: Map aliases explicitly where the agent needs them

node -e "console.log('provide alias map: en to en-US, derived from defaultLocale, not guessed')"

Expected: Aliases resolve deterministically.

Step 4: Re-run extraction for every locale

node scripts/extract-strings.js | tail -3

Expected: All configured locales extract without alias errors.

When to use this

• Extraction fails on locale aliases defined in next.config
• The agent guesses locale lists instead of reading config

When NOT to use this

• The aliases are wrong in next.config itself, fix the config
• Locales resolve but strings are missing, different problem

Tool and version compatibility

• Next.js i18n routing config, next.config.js
• Any extraction agent with configurable locale sources

Variant phrasings

aliases in a custom i18n config file

Same fix. Point the agent at whatever file is authoritative, not its defaults.

domain-based locales

Domains add another alias layer. Resolve domain to locale from the same config block.

Why it happens

Next.js lets the config define the locale list, the default, and domain mappings, but extraction agents often assume a locales folder convention. When the two disagree, aliases the config defines look unresolvable to the agent.

Edge cases

• next.config can be a function, the agent must evaluate it not just parse it
• Middleware can add runtime aliases the config does not show, document those
• Keep one source of truth, config, and make everything read it

Provenance

Resolved from the public thread: https://vectle.com/posts/pstULXOQZ0LJ3c17AxNFn4Qg

Resolved from the public thread: https://vectle.com/posts/pstULXOQZ0LJ3c17AxNFn4Qg

Thread query: extraction agent failed to resolve locale aliases in next.config error

TL;DR: The agent reads locales from one place but your aliases live in next.config, so teach it to read the config. Locale aliases like mapping en to en-US are config, not convention, and the agent guessed wrong. Point the agent at the next.config i18n block and resolve aliases from there.