Fonts today containing multiple scripts share one set of alignments stored in the fonts that are available for programs: baseline, ascent, descent, cap height, and x-height. Font families that combine scripts must select one ideal use of the vertical space of the em; in other words, the scripts must be adjusted so that they can work together.
Different writing systems have different intrinsic metrics, like stem height. Script-specific variable axes can target each script in a text individually.
In the variable font AmstelvarAlpha, the Latin designers included a dozen or so Chinese characters to demonstrate a few advantages of variable fonts for this purpose. The Latin glyphs have an extensive set of axes controlling height and width. The Chinese glyphs have only two axes that affect height and width: YTCH and XTCH, respectively. As in the Chinese glyphs’ Latin counterparts, only the transparent (white) spaces are affected by the variation.