Can we wish Merry Christmas to Christians
If using of such words is for the purpose of congratulating them then it is not correct and it is essential to abstain from it.
Allah knows best.
کما فی الفتاویٰ التاتارخانیة: اجتمع المجوس یوم النیروز فقال مسلم: خوس سیرت نهادہ اند یکفر اھ (۵/ ۵۲۵)