✨ Añade soporte para localización y traducción

- Incluye recursos Fluent básicos y pruebas asociadas.
- Nueva variable de configuración global para definir el idioma
  predeterminado.

src/locale/en-US/test.ftl

@@ -0,0 +1,11 @@
+test-hello-world = Hello world!
+test-hello-user  = Hello, { $userName }!
+test-shared-photos =
+    { $userName } { $photoCount ->
+        [one] added a new photo
+       *[other] added { $photoCount } new photos
+    } of { $userGender ->
+        [male] him and his family
+        [female] her and her family
+       *[other] their family
+    }.