Use lodash's setWith so it always use an object as the namespace.

Close #72.

__tests__/issue72.test.ts

@@ -0,0 +1,10 @@
+import { I18n } from "../src/I18n";
+
+test("works with numeric keys", () => {
+  const i18n = new I18n();
+  i18n.store({ en: { units: { l: "liter", "1": "number" } } });
+
+  expect(i18n.t("units.l")).toEqual("liter");
+  expect(i18n.t("units.1")).toEqual("number");
+  expect(i18n.t("units")).toEqual({ l: "liter", "1": "number" });
+});

src/I18n.ts

@@ -3,6 +3,7 @@
 import get from "lodash/get";
 import has from "lodash/has";
 import set from "lodash/set";
+import setWith from "lodash/setWith";
 
 import {
   DateTime,
@@ -258,7 +259,7 @@ export class I18n {
     const map = propertyFlatList(translations);
 
     map.forEach((path) =>
-      set(this.translations, path, get(translations, path)),
+      setWith(this.translations, path, get(translations, path), Object),
     );
 
     this.hasChanged();

src/lodash.ts

@@ -10,3 +10,4 @@ export { default as flattenDeep } from "lodash/flattenDeep";
 export { default as get } from "lodash/get";
 export { default as has } from "lodash/has";
 export { default as set } from "lodash/set";
+export { default as setWith } from "lodash/setWith";