And knowing more words/languages expands your capability for thought.

Language is more than just some sounds and scribbles that directly translate to person's/places/things. It is very often impossible to express exactly the same thought in a different language because the idea itself has cultural context and meaning imbued by the language.

For example, in English we would say "I like bananas". In Spanish the closest translation is "me gusta bananas," but those are fundamentally two different statements. In English, you are the subject taking affirmative action on the object (banana) by "liking" it. In Spanish, you are instead the passive object being acted upon by the subject (the banana) which is "pleasing" you (gustar ~ to please). Think about that, it seems subtle but consider the implications of being passive, acted upon by the world vs being active, acting up on the world.