feat(admin-*,dashboard): add dashboard i18n extensions

[leobenzol]

Summary

What

Adds functionality to directly export custom translations to be used in the admin dashboard, supporting both "direct" extensions from the main backend project as well as from plugins

Why

It is currently possible to extend the react-i18next instance provided by medusa, but the process is clunky: it requires the same boilerplate component in every plugin and project and the "extender" component must be used in each custom route/widget, since one cant access the common parent scope. See one of my plugins example

How

By creating a new virtual module for i18n, just like other admin features like routes/widgets etc... the DashboardApp now merges all i18n virtual modules into a single "resources" object which is used to initialize the i18n instance directly

Testing

Local testing. Checked extensions in the main project and in plugins(both plugin:develop and plugin:publish) in development and production env.

I noticed now that the other virtual modules have some form of test for the code generation part, should I add one for i18n as well?

---

Examples

Provide examples or code snippets that demonstrate how this feature works, or how it can be used in practice.
This helps with documentation and ensures maintainers can quickly understand and verify the change.

// Example usage

// In src/admin/i18n/index.ts:
import en from "./en.json" with { type: "json" } // "with" clause is mandatory
import fr from "./fr.json" with { type: "json" }

export default {
    en: {
        customNs: en,
        translation: en // will be merged with the default namespace
    },
    fr: {
        customNs: fr,
        translation: fr
    }
}

---

Checklist

Please ensure the following before requesting a review:

• I have added a changeset for this PR
  • Every non-breaking change should be marked as a patch
  • To add a changeset, run yarn changeset and follow the prompts
• The changes are covered by relevant tests
• I have verified the code works as intended locally
• I have linked the related issue(s) if applicable

---

Additional Context

Closes #13698

[changeset-bot]

🦋 Changeset detected

Latest commit: 7459585

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 74 packages

Name	Type
@medusajs/admin-vite-plugin	Patch
@medusajs/admin-bundler	Patch
@medusajs/admin-shared	Patch
@medusajs/dashboard	Patch
@medusajs/medusa	Patch
@medusajs/admin-sdk	Patch
@medusajs/test-utils	Patch
@medusajs/medusa-oas-cli	Patch
integration-tests-http	Patch
@medusajs/draft-order	Patch
@medusajs/analytics	Patch
@medusajs/api-key	Patch
@medusajs/auth	Patch
@medusajs/caching	Patch
@medusajs/cart	Patch
@medusajs/currency	Patch
@medusajs/customer	Patch
@medusajs/file	Patch
@medusajs/fulfillment	Patch
@medusajs/index	Patch
@medusajs/inventory	Patch
@medusajs/link-modules	Patch
@medusajs/locking	Patch
@medusajs/notification	Patch
@medusajs/order	Patch
@medusajs/payment	Patch
@medusajs/pricing	Patch
@medusajs/product	Patch
@medusajs/promotion	Patch
@medusajs/region	Patch
@medusajs/sales-channel	Patch
@medusajs/settings	Patch
@medusajs/stock-location	Patch
@medusajs/store	Patch
@medusajs/tax	Patch
@medusajs/user	Patch
@medusajs/workflow-engine-inmemory	Patch
@medusajs/workflow-engine-redis	Patch
@medusajs/oas-github-ci	Patch
@medusajs/cache-inmemory	Patch
@medusajs/cache-redis	Patch
@medusajs/event-bus-local	Patch
@medusajs/event-bus-redis	Patch
@medusajs/analytics-local	Patch
@medusajs/analytics-posthog	Patch
@medusajs/auth-emailpass	Patch
@medusajs/auth-github	Patch
@medusajs/auth-google	Patch
@medusajs/caching-redis	Patch
@medusajs/file-local	Patch
@medusajs/file-s3	Patch
@medusajs/fulfillment-manual	Patch
@medusajs/locking-postgres	Patch
@medusajs/locking-redis	Patch
@medusajs/notification-local	Patch
@medusajs/notification-sendgrid	Patch
@medusajs/payment-stripe	Patch
@medusajs/core-flows	Patch
@medusajs/framework	Patch
@medusajs/js-sdk	Patch
@medusajs/modules-sdk	Patch
@medusajs/orchestration	Patch
@medusajs/types	Patch
@medusajs/utils	Patch
@medusajs/workflows-sdk	Patch
@medusajs/cli	Patch
@medusajs/deps	Patch
@medusajs/telemetry	Patch
@medusajs/icons	Patch
@medusajs/toolbox	Patch
@medusajs/ui-preset	Patch
create-medusa-app	Patch
medusa-dev-cli	Patch
@medusajs/ui	Patch

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