You're wrapping your two Text components with a Stack component which lays out its children vertically, and you're explicitly specifying that Stack uses zero sp

You're wrapping your two Text components with a Stack component which lays out its children vertically, and you're explicitly specifying that Stack uses zero space between each of its children. This doesn't have anything to do with Thai characters specifically. The glyphs already overlap with common English characters like "j" and punctuation like commas. Moreover, you can get glyphs to overlap between two lines of a normal HTML element with line-height: 1 (and obviously even more easily with line-height less than 1).