I have modified it to :

delete_language_url = self.reverse("update_languages")
            self.browse_to(delete_language_url)
            self.browser.find_element_by_css_selector(".delete-language-button > button[value='de']")

But now the problem is , it doesn't goes to update/languages  instead it goes to register device page first. So, we need to register the device and then we can use this.