implement unit tests to check business logics

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The issue title mentions implementing unit tests for business logic, but the description is empty. First, examine the repository structure to locate existing business logic files and test setup. Look for a `src` or `lib` directory and any existing test files (e.g., using Jest or React Testing Library). Determine what specific logic needs testing, such as locale management or translation functions. Running existing tests can provide context on the testing framework and patterns used.

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