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/merge.ts

@@ -0,0 +1,14 @@
+export function mergeMessageParts(...parts: Array<Record<string, string>>) {
+  const result: Record<string, string> = {}
+
+  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
+}