Use the . It is the most stable, includes online functionality, and updates the car roster to 2015-era vehicles (still old, but newer than 2011).
When the official game died, the modders at TurboDuck and TDU World breathed life back into it. The result is the . tdu2 car pack
These projects provide a custom launcher that restores online functionality and enables DLC content. Unofficial Patch: Use the
This massive update adds over 25+ brand-new vehicles to the game’s dealerships. New Brands: includes online functionality
You must find the "TDU2 DLC Unlocker" or "AutoPack" tools created by modders like Millenium and Speeder.