feat(ui): add locales and split catalogs

Adds Spanish, French, Russian, Japanese, and Simplified Chinese catalogs and wires supported locales into the i18n layer.

packages/ui/src/lib/i18n/messages/en/index.ts

@@ -14,7 +14,7 @@ import { sessionMessages } from "./session"
 import { settingsMessages } from "./settings"
 import { timeMessages } from "./time"
 import { toolCallMessages } from "./toolCall"
-import { mergeMessageParts } from "./merge"
+import { mergeMessageParts } from "../merge"
 
 export const enMessages = mergeMessageParts(
   folderSelectionMessages,

packages/ui/src/lib/i18n/messages/en/merge.ts

@@ -1,25 +0,0 @@
-export type MessageCatalog = Record<string, string>
-
-type MergeParts<Parts extends readonly MessageCatalog[]> = Parts extends readonly [
-  infer Head extends MessageCatalog,
-  ...infer Tail extends MessageCatalog[],
-]
-  ? Head & MergeParts<Tail>
-  : {}
-
-export function mergeMessageParts<const Parts extends readonly MessageCatalog[]>(
-  ...parts: Parts
-): MergeParts<Parts> {
-  const result: Record<string, string> = Object.create(null)
-
-  for (const part of parts) {
-    for (const [key, value] of Object.entries(part)) {
-      if (key in result) {
-        throw new Error(`Duplicate i18n message key: ${key}`)
-      }
-      result[key] = value
-    }
-  }
-
-  return result as MergeParts<Parts>
-}