Version 1.38 is useless without mods for most veteran players. Here is how to find and install compatible mods.
No. TruckersMP only supports the latest stable version of ETS2 (currently 1.49/1.50). If you downgrade to 1.38, you cannot play on official multiplayer servers. Download Euro Truck Simulator 2 1.38
Even with Steam, problems can occur. Here is how to fix the most common errors when downloading ETS2 1.38. Version 1