Quick summary: excavations from the Boğazköy-Hattusha archaeological site (Turkey) unearthed a tablet. That tablet is written mostly in Hittite, but it mentions an idiom from another language, “of the land of Kalašma”, that would be spoken in the northwest of the Hittite empire. Said language would be also Anatolian, so a close-ish relative of Hittite (and Luwian, Palaic, etc.), and ultimately related to Russian, English, Italian, Hindi etc. (it’s all Indo-European).