# i18n guide

vibe_erp is built to be sold worldwide. There are no hard-coded user-facing strings, currencies, date formats, time zones, number formats, address shapes, or tax models in the framework — everything user-facing flows through the i18n and formatting layers from day one. This is guardrail #6 in `CLAUDE.md`, and it applies to the core, every PBC, and every plug-in.

For the architectural placement of i18n, see [`../architecture/overview.md`](../architecture/overview.md) and the full spec at [`../superpowers/specs/2026-04-07-vibe-erp-architecture-design.md`](../superpowers/specs/2026-04-07-vibe-erp-architecture-design.md).

## ICU MessageFormat is the backbone

vibe_erp uses **ICU MessageFormat** (via ICU4J) on top of Spring's `MessageSource`. ICU MessageFormat handles the things naive `printf`-style formatting cannot:

- Plurals (`{count, plural, one {# item} other {# items}}`)
- Gender selection
- Locale-aware number, date, and currency formatting
- Nested arguments and select clauses

A message in a bundle file looks like this:

```properties
orders_sales.cart.summary = {count, plural, =0 {Your cart is empty.} one {# item, total {total, number, currency}} other {# items, total {total, number, currency}}}
```

The same key produces correct output in English, German, Japanese, Chinese, and Spanish without changing a line of calling code.

## Plug-ins ship message bundles

Each plug-in (and each PBC) ships its message bundles inside its JAR under `i18n/<locale>.properties`. The locale tag follows BCP 47:

```
src/main/resources/
└── i18n/
    ├── en-US.properties
    ├── zh-CN.properties
    ├── de-DE.properties
    ├── ja-JP.properties
    └── es-ES.properties
```

The `plugin.yml` manifest lists the bundles so the loader knows to pick them up:

```yaml
metadata:
  i18n:
    - i18n/en-US.properties
    - i18n/de-DE.properties
```

## How the host merges bundles

On boot, and on every plug-in install, the host builds a merged `MessageSource` per locale. The merge order, from lowest precedence to highest:

1. **Core bundles** shipped inside the vibe_erp image.
2. **Plug-in bundles** picked up from `./plugins/*.jar` in plug-in load order. A plug-in may override a core key with the same key in its own bundle, but is not encouraged to.
3. **Tenant overrides** stored in `metadata__translation` rows tagged with the tenant id. These are entered through the Tier 1 customization UI and let an integrator rewrite any string for any tenant without rebuilding anything.

```
tenant overrides   ← highest precedence
   plug-in bundles
   core bundles    ← lowest precedence
```

The merged `MessageSource` is per-locale and per-tenant. Switching the user's locale or switching tenants picks the right merged bundle without restarting anything.

## Shipping locales for v1.0

vibe_erp v1.0 ships with five locales:

| Locale tag | Language |
|---|---|
| `en-US` | English (United States) |
| `zh-CN` | Chinese (Simplified) |
| `de-DE` | German |
| `ja-JP` | Japanese |
| `es-ES` | Spanish (Spain) |

Adding a sixth locale is a Tier 1 operation: drop a `<locale>.properties` file into `i18n-overrides/` on the mounted volume, or add `metadata__translation` rows through the customization UI. No rebuild.

The reference business documentation under `raw/业务流程设计文档/` is in Chinese. **That does not make Chinese the default.** Chinese is one supported locale among the five.

## Translation key naming

Translation keys follow `<plugin-or-pbc>.<area>.<message>`:

```
identity.login.title
identity.login.error.invalid_credentials
catalog.item.field.sku.label
orders_sales.order.status.confirmed
plugin_printingshop.plate.field.thickness.label
```

Rules:

- The first segment is the PBC table prefix (`identity`, `catalog`, `orders_sales`, …) or, for a plug-in, `plugin_<id>`. This is the same prefix used in the database, the metadata `source` column, and the OpenAPI tag.
- Segments are `snake_case`.
- The last segment names the message itself, not the widget that renders it.
- Two plug-ins can never collide: their first segment differs by definition.

## The `Translator` is the only sanctioned way

The host injects a `Translator` (from `org.vibeerp.api.v1.i18n`) into every plug-in endpoint, every workflow task handler, every event listener. **There is no string concatenation in user-facing code, anywhere, ever.**

```kotlin
val message = translator.format(
    MessageKey("orders_sales.order.created.notification"),
    mapOf(
        "orderNumber" to order.number,
        "customerName" to order.customer.name,
        "total" to order.total,
    ),
)
```

What this means in practice:

- A reviewer who sees `"Order " + number + " was created"` in a PR rejects the PR.
- A reviewer who sees a `String.format` against a hard-coded format string rejects the PR.
- A reviewer who sees `if (locale == "en") "..." else "..."` rejects the PR with prejudice.

The `Translator` is locale-aware: it picks up the request's resolved locale from the `LocaleProvider`, which in turn resolves from (in order) the user's profile preference, the request's `Accept-Language`, the tenant default, and the system default.

## PII, dates, numbers, currency

Locale handling does not stop at strings:

- **Dates and times** are formatted through the locale, not through hard-coded patterns. The host exposes locale-aware formatters; plug-ins use them.
- **Numbers** use the locale's grouping and decimal separators.
- **Currency** values are `Money` (from `api.v1.core`) — an amount plus an ISO 4217 code — and the formatter renders them in the user's locale (e.g. `$1,234.56` vs. `1.234,56 €` vs. `¥1,235`).
- **Time zones** are per-tenant and per-user, not per-server.
- **PII fields** are tagged in the field metadata. Tagged fields drive auto-generated DSAR exports and erasure jobs (GDPR Articles 15/17), and the audit log records access to them when audit-strict mode is on.
- **Address shapes** are not assumed. There is no "state/province" or "ZIP code" hard-coded in the core; address fields are configurable via metadata so a Japanese address can have prefecture/city/ward and a French address can have arrondissement.

## Where to go next

- Plug-in author walkthrough that uses `Translator`: [`../plugin-author/getting-started.md`](../plugin-author/getting-started.md)
- Plug-in API surface for i18n: [`../plugin-api/overview.md`](../plugin-api/overview.md)