fix(core): resolve type mismatch in useGetLocale hook

.changeset/heavy-berries-appear.md

@@ -0,0 +1,9 @@
+---
+"@refinedev/core": patch
+---
+
+- Throw an error in `useGetLocale` if it is called without an i18n Provider.
+- This ensures the hook's return type matches that of `i18nProvider.getLocale`.
+- `useTranslation().getLocale` which is from `useGetLocale` now returns a string.
+
+[Resolves #6812](https://github.com/refinedev/refine/issues/6812)

packages/core/src/hooks/i18n/useGetLocale.spec.tsx

@@ -4,10 +4,12 @@ import { useGetLocale } from "@hooks";
 import { TestWrapper } from "@test";
 
 describe("useGetLocale", () => {
-  it("should get undefined value if i18n provider not defined", () => {
-    const { result } = renderHook(() => useGetLocale());
+  it("should throw error if i18n provider is not defined", () => {
+    const result = () => renderHook(() => useGetLocale());
 
-    expect(result.current()).toBe(undefined);
+    expect(result).toThrow(
+      "useGetLocale cannot be called without i18n provider being defined.",
+    );
   });
 
   it("should get locale value from i18nProvider getLocale method", () => {

packages/core/src/hooks/i18n/useGetLocale.ts

@@ -2,7 +2,7 @@ import { useCallback, useContext } from "react";
 
 import { I18nContext } from "@contexts/i18n";
 
-export type UseGetLocaleType = () => () => string | undefined;
+export type UseGetLocaleType = () => () => string;
 
 /**
  * If you need to know the current locale, refine provides the `useGetLocale` hook.
@@ -13,5 +13,11 @@ export type UseGetLocaleType = () => () => string | undefined;
 export const useGetLocale: UseGetLocaleType = () => {
   const { i18nProvider } = useContext(I18nContext);
 
-  return useCallback(() => i18nProvider?.getLocale(), []);
+  if (!i18nProvider) {
+    throw new Error(
+      "useGetLocale cannot be called without i18n provider being defined.",
+    );
+  }
+
+  return useCallback(() => i18nProvider.getLocale(), []);
 };