So, I was thinking about where to put this question. It has linguistic and political aspects but it also has an impact on many other topics. At the end, I also think that it can't be answered with facts alone, which is why I write my question here.
Let's imagine that languages which are quite close to each other (let's take Germanic languages without English as example). For the sake of this question, these languages have not had any written standard before, so people are not influenced by one way or the other and no books and other media has a written form. These languages agree to create a standard orthography, so a standard way of writing down what is spoken, but no standard dictionary.
I have my thoughts of what could happen, but I would like to hear the logical conclusions of other people.
Edit: I'm especially looking for things the governments would have to implement, how the spread of education of the writing would happen, how people would try to understand one another and so on.