Vocabulary size is a topic that can lead to all sorts of heated discussions, hurt feelings, unjustified pride, and never-ending debates. The reason why this is so is because having a large vocabulary size is often seen as being an enviable trait, whilst discovering that one has merely an average vocabulary size, which, by definition, most people do, leaves many people feeling that they need to reach for a dictionary and start learning some new words. So what is it about vocabulary size that makes it so important to measure? Why bother making an entire website devoted to testing vocabulary knowledge?
For an international project like this, I’d like to attract as wide an audience as possible to investigate the course of vocabulary acquisition and compare that course across different native languages (L1). Certainly the course would be different for language learners whose L1s are cognate with the target language (L2) they are studying. And for those that are not cognate, there are probably differences among them as well depending on factors such as the degree of similarity between the two languages’ phonemic inventories, morphological typologies, and even writing systems. Even the prevalence of L1 loan words in active use in the target L2 may affect the course of vocabulary acquisition.
There is a fundamental problem with many, perhaps most, vocabulary tests which is rarely acknowledged. It's not always clear what the problem is because intuition tells us that testing knowledge of a word should be easy and the result should be unambiguous; either one knows a word or does not. But the reality is much more complicated than that.