Fixes: 1) Corrected `ForeignKey` type assertions across models; 2) Resolved typos and formatting inconsistencies in `.env` and README; 3) Fixed explicit boolean checks in user manager methods.
Extra: Updated type hints in multiple models, serializers, and views.
Fixes: 1) Update locale codes in `deepl_translate.py` to lowercase for consistency.
Extra: 1) Minor refactoring to ensure compatibility and avoid undefined behavior in slug population logic.