conlang
Explanation
This comic centers on a constructed language ("conlang") club meeting. A member proudly announces: "It's a tonal language! Four tones. The mark of a truly rich vocabulary is a single three-word consisting of three identical syllables."
Outside the club building, someone asks: "Are you going to a stupid grownup birthday party right now?"
The next panel shows the conlang club in action, with everyone saying "Cheery, cheery, cheery" -- which is apparently a meaningful phrase in their constructed language due to tonal differences, but sounds to an outsider like meaningless repetition.
When asked "What makes you say that?" about the birthday party accusation, the implication is clear: a group of adults sitting around saying "cheery cheery cheery" looks indistinguishable from a children's party game.
The humor targets the niche hobby of constructing artificial languages (conlanging), poking fun at how an activity that its practitioners consider intellectually rigorous and linguistically sophisticated can look absurd to outsiders. The joke about tonal languages is rooted in real linguistics -- languages like Mandarin Chinese use tones to distinguish meaning, so the same syllable pronounced with different tones can mean entirely different things. But to an untrained ear, it just sounds like someone repeating themselves. The comic affectionately mocks the gap between the conlanger's internal experience of linguistic richness and the external perception of grown adults making silly sounds.