test: add comprehensive unit tests for loader.js (#5033)

* test: add comprehensive unit tests for loader.js

- Add test coverage for requirejs configuration
- Test i18next initialization and language switching
- Mock external dependencies (i18next, requirejs-plugins)
- Handle async initialization logic

* style: fix formatting in loader.test.js

* style: update copyright year to 2026

* style: run prettier on loader.test.js

Author: Ashutoshx7