Thought. Before language, people would start thinking already, right? As long as your brain is active, you're thinking. The first people would start thinking first, before they invented language. This is my interpretation of the question, and it's pretty clear which one came first to me.
Exactly, you can only think through a medium, without that medium, thoughts would have no essence, that's why I believe language and thought came together.
Animals still assign certain things a "value". They still use a form of language, just not one that we do.
You need to think before you communicate or do pretty much anything, that applies to animals as well.
The general term for language is a means of communication, but anthropologists also say that language is also how a person thinks, try to think of something without using language, it is impossible, because the essence of thought relies on language.