fix: preserve custom nodes i18n data when locales are lazily loaded (#7214)

## Summary
Custom nodes can provide localized translations via their locales
folder.
After the switch to lazy-loading locales (only English pre-loaded),
custom node i18n data was being lost because:
1. loadCustomNodesI18n() merges data before locale is loaded
2. loadLocale() uses setLocaleMessage() which overwrites everything

Solution: Store custom nodes i18n data and re-merge it after each
lazy-loaded locale completes loading.

- Add mergeCustomNodesI18n() function to store and merge custom data
- Modify loadLocale() to re-merge stored data after loading
- Add unit tests for the i18n merging behavior

fix #7025

## Screenshots (if applicable)
<img width="706" height="1335" alt="image"
src="https://github.com/user-attachments/assets/41e4ba2c-b4c0-4d0d-a104-1ede8939ff92"
/>
<img width="672" height="1319" alt="image"
src="https://github.com/user-attachments/assets/6c3e55e5-20d2-4093-a86a-7496db3dfe94"
/>

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7214-fix-preserve-custom-nodes-i18n-data-when-locales-are-lazily-loaded-2c26d73d3650812fab31edd71cf51a19)
by [Unito](https://www.unito.io)

Author: jtydhr88

src/components/graph/GraphCanvas.vue

@@ -132,7 +132,7 @@ import { useCopy } from '@/composables/useCopy'
 import { useGlobalLitegraph } from '@/composables/useGlobalLitegraph'
 import { usePaste } from '@/composables/usePaste'
 import { useVueFeatureFlags } from '@/composables/useVueFeatureFlags'
-import { i18n, t } from '@/i18n'
+import { mergeCustomNodesI18n, t } from '@/i18n'
 import { LiteGraph } from '@/lib/litegraph/src/litegraph'
 import { useLitegraphSettings } from '@/platform/settings/composables/useLitegraphSettings'
 import { CORE_SETTINGS } from '@/platform/settings/constants/coreSettings'
@@ -391,9 +391,7 @@ useEventListener(
 const loadCustomNodesI18n = async () => {
   try {
     const i18nData = await api.getCustomNodesI18n()
-    Object.entries(i18nData).forEach(([locale, message]) => {
-      i18n.global.mergeLocaleMessage(locale, message)
-    })
+    mergeCustomNodesI18n(i18nData)
   } catch (error) {
     console.error('Failed to load custom nodes i18n', error)
   }

src/i18n.test.ts

@@ -0,0 +1,200 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+const { i18n, loadLocale, mergeCustomNodesI18n } = await import('./i18n')
+
+// Mock the JSON imports before importing i18n module
+vi.mock('./locales/en/main.json', () => ({ default: { welcome: 'Welcome' } }))
+vi.mock('./locales/en/nodeDefs.json', () => ({
+  default: { testNode: 'Test Node' }
+}))
+vi.mock('./locales/en/commands.json', () => ({
+  default: { save: 'Save' }
+}))
+vi.mock('./locales/en/settings.json', () => ({
+  default: { theme: 'Theme' }
+}))
+
+// Mock lazy-loaded locales
+vi.mock('./locales/zh/main.json', () => ({ default: { welcome: '欢迎' } }))
+vi.mock('./locales/zh/nodeDefs.json', () => ({
+  default: { testNode: '测试节点' }
+}))
+vi.mock('./locales/zh/commands.json', () => ({ default: { save: '保存' } }))
+vi.mock('./locales/zh/settings.json', () => ({ default: { theme: '主题' } }))
+
+describe('i18n', () => {
+  beforeEach(async () => {
+    vi.resetModules()
+  })
+
+  describe('mergeCustomNodesI18n', () => {
+    it('should immediately merge data for already loaded locales (en)', async () => {
+      // English is pre-loaded, so merge should work immediately
+      mergeCustomNodesI18n({
+        en: {
+          customNode: {
+            title: 'Custom Node Title'
+          }
+        }
+      })
+
+      // Verify the custom node data was merged
+      const messages = i18n.global.getLocaleMessage('en') as Record<
+        string,
+        unknown
+      >
+      expect(messages.customNode).toEqual({ title: 'Custom Node Title' })
+    })
+
+    it('should store data for not-yet-loaded locales', async () => {
+      const { i18n, mergeCustomNodesI18n } = await import('./i18n')
+
+      // Chinese is not pre-loaded, data should be stored but not merged yet
+      mergeCustomNodesI18n({
+        zh: {
+          customNode: {
+            title: '自定义节点标题'
+          }
+        }
+      })
+
+      // zh locale should not exist yet (not loaded)
+      const zhMessages = i18n.global.getLocaleMessage('zh') as Record<
+        string,
+        unknown
+      >
+      // Either empty or doesn't have our custom data merged directly
+      // (since zh wasn't loaded yet, mergeLocaleMessage on non-existent locale
+      // may create an empty locale or do nothing useful)
+      expect(zhMessages.customNode).toBeUndefined()
+    })
+
+    it('should merge stored data when locale is lazily loaded', async () => {
+      // First, store custom nodes i18n data (before locale is loaded)
+      mergeCustomNodesI18n({
+        zh: {
+          customNode: {
+            title: '自定义节点标题'
+          }
+        }
+      })
+
+      await loadLocale('zh')
+
+      // Verify both the base locale data and custom node data are present
+      const zhMessages = i18n.global.getLocaleMessage('zh') as Record<
+        string,
+        unknown
+      >
+      expect(zhMessages.welcome).toBe('欢迎')
+      expect(zhMessages.customNode).toEqual({ title: '自定义节点标题' })
+    })
+
+    it('should preserve custom node data when locale is loaded after merge', async () => {
+      // Simulate the real scenario:
+      // 1. Custom nodes i18n is loaded first
+      mergeCustomNodesI18n({
+        zh: {
+          customNode: {
+            title: '自定义节点标题'
+          },
+          settingsCategories: {
+            Hotkeys: '快捷键'
+          }
+        }
+      })
+
+      // 2. Then locale is lazily loaded (this would previously overwrite custom data)
+      await loadLocale('zh')
+
+      // 3. Verify custom node data is still present
+      const zhMessages = i18n.global.getLocaleMessage('zh') as Record<
+        string,
+        unknown
+      >
+      expect(zhMessages.customNode).toEqual({ title: '自定义节点标题' })
+      expect(zhMessages.settingsCategories).toEqual({ Hotkeys: '快捷键' })
+
+      // 4. Also verify base locale data is present
+      expect(zhMessages.welcome).toBe('欢迎')
+      expect(zhMessages.nodeDefs).toEqual({ testNode: '测试节点' })
+    })
+
+    it('should handle multiple locales in custom nodes i18n data', async () => {
+      // Merge data for multiple locales
+      mergeCustomNodesI18n({
+        en: {
+          customPlugin: { name: 'Easy Use' }
+        },
+        zh: {
+          customPlugin: { name: '简单使用' }
+        }
+      })
+
+      // English should be merged immediately (pre-loaded)
+      const enMessages = i18n.global.getLocaleMessage('en') as Record<
+        string,
+        unknown
+      >
+      expect(enMessages.customPlugin).toEqual({ name: 'Easy Use' })
+
+      await loadLocale('zh')
+      const zhMessages = i18n.global.getLocaleMessage('zh') as Record<
+        string,
+        unknown
+      >
+      expect(zhMessages.customPlugin).toEqual({ name: '简单使用' })
+    })
+
+    it('should handle calling mergeCustomNodesI18n multiple times', async () => {
+      // Use fresh module instance to ensure clean state
+      vi.resetModules()
+      const { i18n, loadLocale, mergeCustomNodesI18n } = await import('./i18n')
+
+      mergeCustomNodesI18n({
+        zh: { plugin1: { name: '插件1' } }
+      })
+
+      mergeCustomNodesI18n({
+        zh: { plugin2: { name: '插件2' } }
+      })
+
+      await loadLocale('zh')
+
+      const zhMessages = i18n.global.getLocaleMessage('zh') as Record<
+        string,
+        unknown
+      >
+      // Only the second call's data should be present
+      expect(zhMessages.plugin2).toEqual({ name: '插件2' })
+      // First call's data is overwritten
+      expect(zhMessages.plugin1).toBeUndefined()
+    })
+  })
+
+  describe('loadLocale', () => {
+    it('should not reload already loaded locale', async () => {
+      await loadLocale('zh')
+      await loadLocale('zh')
+
+      // Should complete without error (second call returns early)
+    })
+
+    it('should warn for unsupported locale', async () => {
+      const consoleSpy = vi.spyOn(console, 'warn').mockImplementation(() => {})
+
+      await loadLocale('unsupported-locale')
+
+      expect(consoleSpy).toHaveBeenCalledWith(
+        'Locale "unsupported-locale" is not supported'
+      )
+      consoleSpy.mockRestore()
+    })
+
+    it('should handle concurrent load requests for same locale', async () => {
+      // Start multiple loads concurrently
+      const promises = [loadLocale('zh'), loadLocale('zh'), loadLocale('zh')]
+
+      await Promise.all(promises)
+    })
+  })
+})

src/i18n.ts

@@ -94,6 +94,9 @@ const loadedLocales = new Set<string>(['en'])
 // Track locales currently being loaded to prevent race conditions
 const loadingLocales = new Map<string, Promise<void>>()
 
+// Store custom nodes i18n data for merging when locales are lazily loaded
+const customNodesI18nData: Record<string, unknown> = {}
+
 /**
  * Dynamically load a locale and its associated files (nodeDefs, commands, settings)
  */
@@ -137,6 +140,10 @@ export async function loadLocale(locale: string): Promise<void> {
 
       i18n.global.setLocaleMessage(locale, messages as LocaleMessages)
       loadedLocales.add(locale)
+
+      if (customNodesI18nData[locale]) {
+        i18n.global.mergeLocaleMessage(locale, customNodesI18nData[locale])
+      }
     } catch (error) {
       console.error(`Failed to load locale "${locale}":`, error)
       throw error
@@ -150,6 +157,24 @@ export async function loadLocale(locale: string): Promise<void> {
   return loadPromise
 }
 
+/**
+ * Stores the data for later use when locales are lazily loaded,
+ * and immediately merges data for already-loaded locales.
+ */
+export function mergeCustomNodesI18n(i18nData: Record<string, unknown>): void {
+  // Clear existing data and replace with new data
+  for (const key of Object.keys(customNodesI18nData)) {
+    delete customNodesI18nData[key]
+  }
+  Object.assign(customNodesI18nData, i18nData)
+
+  for (const [locale, message] of Object.entries(i18nData)) {
+    if (loadedLocales.has(locale)) {
+      i18n.global.mergeLocaleMessage(locale, message)
+    }
+  }
+}
+
 // Only include English in the initial bundle
 const messages = {
   en: buildLocale(en, enNodes, enCommands, enSettings)