CJK usually needs no extra tracking; the em box already holds the gap

What it is

Han glyphs are drawn inside a square em box whose left and right side bearings are already the gap. Set those boxes adjacent and the seam is native to the face, not a missing layer of letter-spacing. Adding tracking to a Chinese paragraph tears a second seam on top of one that was already budgeted, and reading shifts from naming characters to counting unrelated squares. Latin lacks that built-in seam, which is why it needs tracking. Copying the Latin habit onto Han is repairing a hole that is not there.

Why it happens

Few Han glyphs reach all four edges of the em; the left and right padding is the type designer’s buffer for the neighbour. In horizontal setting, two boxes side by side already yield a visual gap of roughly both bearings, scaling linearly with type size, no extra coefficient required. letter-spacing in Chinese inserts a third gap between boxes. It does not participate in the glyph’s centre of gravity; it only thins the line. Chinese also has no word spaces to absorb that gap, so opening tracking does not “loosen the word” — it islands every character and leaves segmentation to the reader’s head. Punctuation hanging and end-of-line compression are local surgeries on the box. They are not paragraph tracking.

Where it stops holding

Very small Han (captions, map labels) sometimes needs a little extra seam or strokes fuse; that is a discriminability patch, not a body default. Display titles with ornaments between characters are graphic setting. In mixed CJK–Latin, the Latin run still follows Latin tracking; do not add the same letter-spacing to the Han “for consistency.” Vertical Han uses the same mechanism on the up–down axis: the em already has head and foot bearings, and letter-spacing rips along the line.

Applying it

• Leave Chinese body letter-spacing at the face default (usually zero). Do not inherit an open track from a Latin display style.
• Set the same passage twice: default, and 0.1em added. If the opened version reads like counting squares, that style does not belong on Chinese paragraphs.
• Hunt the cascade: a global * { letter-spacing: … } or a style copied from an English component is how Chinese gets hit by accident.

Related

• Same group: F4.12.1 Tracking that is too tight collides glyphs; too loose breaks the word · F4.12.3 All-caps and small type need extra tracking to stay distinguishable · F4.12.4 Uneven word spacing in justified Latin runs creates rivers
• Nearby: F4.06 Mixed CJK and Latin typesetting · F4.14 Punctuation and kinsoku
• Search terms: em box · CJK tracking · side bearing