The largest languages in the world, based on the number of words in their largest dictionaries, are English, German, Russian, French and Spanish. I have studied all of them, even though my Russian only goes as far as learning the Cyrillic alphabet and a few Russian phrases.
The numbers are:
English – 616,000 words
German – 185,000 words
Russian – 130,000 words
Spanish – 100,000 words
French – 100,000 words
Being an English speaker, I am amazed that the English vocabulary is more than three times that of the next largest language, German. The average English speaker only recognizes 10,000 to 20,000 words, and the average active vocabulary is only about 1,000 to 4,000 words.