No, it's definitely not illegal. A large majority of the rules restricting the Kurdish language/culture were dumped several years ago when Turkey started talks to enter the EU. Now, the official language of Turkey is Turkish (similar to how the official language of the U.S. should be English IMO), but Kurds are free to speak their language, and they do.
And if you feel Turkey is getting a "free pass" because they're allies, then should Kurdish terrorists get a free pass because Kurds are an ally?
And if you feel Turkey is getting a "free pass" because they're allies, then should Kurdish terrorists get a free pass because Kurds are an ally?Certainly, for the same reasons that people forgave Mandela and the ANC for using terrorism in South Africa. Using terrorism when you're under occupation and oppression is inherently more legitimate than when you're the occupying power. That's why terrorism against the Russians in Afghanistan is forgiven and terrorism by Saddam against the Shi'ites and Kurds isn't.
Given that Turkey was organized as a national state after the collapse of the Ottoman Empire, the Kurdish population is a bit like the Arabs in Israel. Except that the Kurds and Turks share the same religion.