What is the difference between the Croatian and the Serbian language?
The difference is small (it’s more of a dialectal difference, so the speakers can understand each other well) – there is a very good article on this topic on Wikipedia ☺ Even though the two languages (and others in the region that are now known as Montenegrin or Bosnian) are very similar to each other, speakers in different locations can be sensitive to these differences. So, especially if you need a text for business purposes, you should pay attention to this issue.