This is a question I’m often asked by people who haven’t come across type design before.
Letters are unique in their use and quite unlike any other representational form. A seasoned type designer realises that one is not exactly focusing on the individual shape of each letter, though that does come into it, but more closely scrutinising how the letters set together. Each letter has to fit with every other letter in a regular rhythm to enable the reader to parse the wordshapes into meaningful semantic content. At the same time, the type designer has the difficult job of balancing the opposing goals of unique characteristics (to attract people to the typeface) and readability (which requires the letterforms to be unintrusive and to facilitate the most direct reading experience without catching the reader’s eye on unexpected details).
What this means is that designing type (at least text type) is about seeing how shapes fit together in a consistent pattern with a degree of visual interest that is necessarily subtle. The design brief will certainly define other characteristics, such as the typeface’s intended usage size, mood and tone, set width, length of extenders and more.
In the title question, of course, there’s the hidden problem in the conflation of language with writing system, which is a common mistake, though it should not be difficult to see that the Latin writing system is used for many language families across Europe from Finland to Portugal. There are language-specific writing systems like Armenian or Thai; also there are language-specific variations of a writing system, like Bulgarian variant forms in Cyrillic.
And this is where the next level of detail arises in designing scripts for other languages. A language and a writing system are closely related. Although they use the same script, Finnish sentences and Portuguese sentences look very different on the page. Finnish has a high proportion of double letters (geminates), a lot of diagonal letters (kvwxy), and a grammar which means words can be very long (agglutination). Portuguese, like other Romance languages, favours the round letters (acdegopsu) and uses accents like the acute, cedilla, circumflex and tilde. If writing systems are musical instruments, the languages they play are different genres of music, with different rhythms and chords. But the music they play cannot sound harmonious if the instruments are badly designed.
The job of the type designer, then, is like the job of the violin maker. The craftsperson carefully assembles the instrument from components that have been designed to work together to resound with a pleasant tone, and to allow violinists to play the notes and chords they expect when bowing the strings. The maker does not need to know all the pieces of music that are going to be played on the violin, but does need tacit knowledge (one would assume) of timbre, harmonics, resonance and ergonomics. In the same way, the type designer needs to gain a familiarity with the writing system, to recognise how the language makes the letters look together, to learn to see the letters as letters rather than just as shapes, and to see whether every letter sings with the same voice.
This means keeping a keen eye on the way the letters compose typographically into words and paragraphs, staying focused on achieving even colour and spacing, and implementing consistent forms and styling. The group of letters needs to follow clear gestures that make each letter what it is. (‘Gestures’ is not quite an ideal word, since constructed typefaces, not based on handwriting, are a worthwhile genre to explore. What I mean is that each letter has identifiable stems, arches, bowls, loops, junctions, counters or apertures that makes it different to the other letters.) In my view, the difference between a mediocre typeface and an excellent one is the amount of time the designer has put into regularising and unifying all these disparate shapes into smooth conformity. Notice that none of these factors directly requires knowing any vocabulary.
People learning exotic languages need to learn the new alphabet before they can start reading. What this means is that on some level, we learn to recognise the letters separately from the words they build. It’s also true for languages that use our mother writing system: a language like Basque may be unknown to most outside Spain even though many people are familiar with the Latin writing system it uses. This is exactly the same familarity type designers need: recognising the letters as letters, and maybe ‘reading’ the letters without necessarily attributing semantic content to the words.
Of course, the designer obtains markedly more convincing results when informed about relative letter frequencies, common letter combinations, and the relative importance of marks. It certainly takes time to thoroughly research a script and build this knowledge. The designer needs to study handwriting from different hands, fully understand and internalise the ‘gestures’ of each letter or component, and explore a wide range of existing typefaces to see how the essentials and idiosyncrasies of written forms have been conventionally converted into typographic forms.