In Suriname today, Dutch is the sole official language, and over 60 percent of the population speaks it as a mother tongue. Dutch is the obligatory medium of instruction in schools in Suriname, even for non-native speakers. A further twenty-four percent of the population speaks Dutch as a second language. Suriname gained its independence from the Netherlands in 1975 and has been an associate member of the Dutch Language Union since <answer>2004</answer>. The lingua franca of Suriname, however, is Sranan Tongo, spoken natively by about a fifth of the population.
What year did Suriname join the Dutch Language Union?
2004