In writing, Vietnamese relies heavily on diacritical marks. To create legible and readable Vietnamese typefaces, the marks not only need to be clear and balanced with the base glyphs, they also must not disrupt the kerning and leading of the overall design. This chapter focuses on the typographic details to help designers see the interaction between the letters and the diacritics.
An acute (dấu sắc) and a grave (dấu huyền) must have the same form. The former signifies the rising tone and the latter signifies the falling tone; therefore, they must reflect each other. On both accents, their bottoms are narrower than their tops. In relation to their base letter, an acute is positioned slightly right and a grave is positioned slightly left. Both accents must not extend beyond their base glyphs.
A circumflex is shaped like a chevron with thick stroke at the top and thinner strokes at the bottoms. It has the same form as a caron, which is not used in Vietnamese, but flipped. The joining of an acute and a grave can create a circumflex, but modifications are needed to produce a symmetrical stroke. In most cases, a circumflex is symmetrical, but it can also be asymmetric and stressed downward. To avoid kerning issues, a circumflex must not be wider than its base letter. When combined, its form can be modified to work well with another mark (acute, grave, hook above, or tilde).
A breve is curved and must not be mistaken for a pointed caron, which does not exist in the Vietnamese writing system. It should not attach to the base letter and interfere with another diacritical mark (acute, grave, hook above, or tilde). The bottom curve of a breve should be thicker than the two upper ends. Its form can be adjusted when combined with another mark.
A horn must be attached to the letter o or the letter u. Its stroke begins from the upper right of the base letter and leads upward. Although appending a horn at the top of the u creates a seamless integration, attaching a horn lower on the stem of the u is also acceptable. Consistency and balance (with acute, grave, hook above, and tilde) are important when determining the position of a horn.
Although a hook above looks like a question mark without the dot, the former must be smaller than the latter and the bottom stem of a hook must be truncated. A hook must always be positioned above a circumflex, a breve, or a horn. When set together, they need to work in harmony.
A tilde (dấu ngã) has a symmetrical form because its structure derives from the letter N. As with the letter N, the strokes on both ends are smaller than the middle curve.1 A tilde is always positioned above a vowel, a circumflex, a breve, or a horn; therefore, they must work in harmony.
For consistency, an underdot (dấu nặng) can be identical to the period and the dot on the letter i. Otherwise an underdot must be smaller than the period. Its placement must be centered directly below the base letter. In some cases with the letter y, a dot can be placed slightly right to avoid clashing with the descender.
When designing the letter Đ (uppercase) and đ (lowercase), the thickness, length, and position of the cross bar play a crucial role in legibility. If the bar is too thin, legibility is compromised at small sizes. To avoid kerning issues, the length of the bar must not extend too far from its base. In a serif typeface, the bar can only exceed slightly beyond its serif. For the letter Đ, the bar needs to be shorter on the left and longer on the right. In contrast, the bar on the letter đ needs to be longer on the left and shorter on the right.
In Vietnamese, the bar on the letter Đ must be positioned in the middle of the cap height. The Vietnamese writing system has no overdot, palatal hook, macron, underdot or undercomma with the letter D.
In the following example, the third uppercase Đ (right) from Alegreya Sans had the bar placed above, which was incorrect. I reached out to Juan Pablo del Peral who designed the Alegreya family and he made the update, which is the middle Đ in the illustration.
The đồng is the official currency of Vietnam. Its symbol, ₫, is made of the lowercase đ and a line at the bottom. The line can be placed above, below, or on the baseline. The lowercase đ (for ₫) can be ten to fifteen percent smaller the than regular letter if the bottom line is on or above the baseline.