Language is the structure of thought. It shapes and limits what we think, and therefore how we act. Therefore, a larger vocabulary means you're capable of deeper, more thorough thought. Life becomes complex. The more words you know, the more you understand what is going on around you.
French is directional in language, German is descriptive, English is active verbal, some native traditional languages focus on the texture of substance, and all of these languages invariably impact the way these populations think, and hence act. Learning more than one language can potentially expand how you think, but this only comes at a masterly level. You have to become so fluent in each language, that you can switch from one to the other easily, and appreciate what each language gives you.
A lot of communication is non-verbal, but language is basically the foundation in which a fully formed "thought" is catalyzed or built, impacting even the non-verbal understanding of such.
We have memories from before we could speak or walk. We only have those memories because we looked back after we had a grasp of language and brought those memories into a more capable consciousness. Only the most potent moments before language will be remembered, because they were burned into long term memory. The mind continuously recycles sensory and memory data. Thus you learn.
Symbolic thought happens, but we don't start out that way. We learn associations, we don't come pre-programmed with them. There is never a time without symbols. Images in the mind is the internal representation of external sensed reality. The agreed linguistic language is a social contract to agree on a particular sound to convey an object or concept within a group.