fix(frontend): improve performance by caching translated texts

Signed-off-by: Tilman Vatteroth <git@tilmanvatteroth.de>

frontend/src/hooks/common/useTranslatedText.spec.ts

@@ -0,0 +1,42 @@
+/*
+ * SPDX-FileCopyrightText: 2023 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+import { useTranslatedText } from './use-translated-text'
+import { renderHook } from '@testing-library/react'
+import type { Namespace } from 'i18next'
+import * as ReactI18NextModule from 'react-i18next'
+import type { UseTranslationResponse } from 'react-i18next'
+import { Mock } from 'ts-mockery'
+
+jest.mock('react-i18next')
+
+describe('useTranslatedText', () => {
+  const mockTranslation = 'mockTranslation'
+  const mockKey = 'mockKey'
+  let translateFunction: jest.Mock
+
+  beforeEach(() => {
+    translateFunction = jest.fn(() => mockTranslation)
+    const useTranslateMock = Mock.of<UseTranslationResponse<Namespace, unknown>>({
+      t: translateFunction
+    })
+    jest.spyOn(ReactI18NextModule, 'useTranslation').mockReturnValue(useTranslateMock)
+  })
+
+  it('translates text', () => {
+    const { result } = renderHook(() => useTranslatedText(mockKey))
+
+    expect(result.current).toBe(mockTranslation)
+    expect(translateFunction).toBeCalledWith(mockKey)
+  })
+
+  it('translates text with options', () => {
+    const mockOptions = {}
+    const { result } = renderHook(() => useTranslatedText(mockKey, mockOptions))
+
+    expect(result.current).toBe(mockTranslation)
+    expect(translateFunction).toBeCalledWith(mockKey, mockOptions)
+  })
+})