Two orcs
Officially better than you, according to PoN
I take the exact opposite approach, having monsters clearly speak their alien minds. It's very much in the style of Jack Vance, where the predatory deodands will knock on your door and plead with you to open it because they are hungry. Scrutability makes them more playable too as there is levers to pull to get diplomacy going (or it's possible to realize no compromise is possible). Last session, the players ran into some spell spiders and got a friendly reaction roll. After a bit of back and forth they decide to trade away a scroll for silver and having one of the spell spiders guide them invisibly to another location in the dungeon. The spell spiders have human-like hands and fondle their fangs when they get excited.Whenever I include a monster race that I want my players to find "alien enough", I make them speak in a language that can't be understood without magic.
Mage: Can I inquire, master Weaver, what will you do with the scroll? Eat it?
Spider: You insult me, wizard. Like all civilized people we eat only liquified flesh.