Not counting Toki Pona (which is a constructed language), what languages in use today have the smallest vocabularies?

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Every few years or so, I develop a curiosity about linguistics and the make up of languages. For a long time I have wondered if there is a such a thing as a "minimum theoretical number of vocabulary words" necessary to convey almost all thoughts. It seems to me that most languages have far more vocabulary words than is necessary to conduct conversations and express ideas. Over time, many words fall out of use.

If it helps, readers should know that I am not a linguist by any means. All I claim to know are two and a half languages. Your answer to this question may more than satisfy mere curiosity.