For many people who speak more than one language, their language proficiency for each of the languages varies. We can conjecture that people who use one language (primary language) more than another would show higher language proficiency in that primary language. It is, however, difficult to observe and quantify that problem because natural language use is difficult to collect in large amounts. We identify Wikipedia as a great resource for studying multilingualism, and we conduct a quantitative analysis of the language complexity of primary and non-primary users of English, German, and Spanish. Our preliminary results indicate that there are indeed consistent differences of language complexity in the Wikipedia articles chosen by primary and non-primary users, as well as differences in the edits by the two groups of users.