To have a good relation with vendors I think you need to be able to communicate with them appropriately and this includes language barrier. As was seen in this simulation, the language barrier really complicated everything. Additionally to make communication more effective clear documentation of everything should be kept. You need to specify exactly what you want and leave no room for interpretation. Of course being cordial is also a must. But you want to make sure that the vendor you are using meets all the standards that you have set for your project or company. Using a vendor that isn’t certified might not be a good idea so certifications should be checked prior. Transparency is the key in my opinion.