The perfect subtitle is one you don’t notice. Occasionally, you might thrill to Anthony Burgess’s English subtitles in alexandrine form for Cyrano de Bergerac (1990), or marvel at the bravura way Timur Bekmambetov threads animated subtitles into Night Watch (2004), or chuckle at the gaffes on old Hong Kong movies (“I have captured you by the short rabbits”). But mostly you just speed-read and move on.

This year, however, subtitles have been attracting more attention than usual. In January, Alfonso Cuarón condemned Netflix’s decision to add Castilian-Spanish subs to his film Roma as “parochial, ignorant and offensive to Spaniards”, who presumably couldn’t be trusted to understand the Mexican accent. Two days later, the Castilian subtitles were removed.

But criticism of Roma’s subtitles didn’t stop there. In February, the ATAA (Association des Traducteurs/Adaptateurs de l’Audiovisuel) pointed out that the film’s French subtitles were full of grammatical errors, spelling mistakes and mistranslations. The ATAA’s chairperson, Ian Burley, who has been subtitling French, Belgian and Italian movies for more than 30 years, also took a look at Roma’s English subtitles, and found them riddled with stylistic inconsistencies, sloppy synchronisation and clumsy line breaks or punctuation, all of which are liable to distract or discombobulate the viewer. And in the riot scene, a woman’s desperate exhortation of “Vamos!” (“Come on!”) to a dying man whose head she is cradling is clumsily translated as “Let’s go!” – as though she thinks he is dawdling.

Concerned not just by the problems with Roma, well publicised because of the Oscar-winning film’s high profile, but by a more general decline in subtitling standards, AVTE (AudioVisual Translators Europe) is collaborating with its member associations (including the British Subtitlers’ Association, Subtle) in a call for film-makers to cooperate more closely with professional subtitlers, reminding them that subtitling is a craft – an art, even – that ought not to be left to amateurs or automatic translation software.

Anthony Burgess’s subtitles for Cyrano de Bergerac won praise for their alexandrine form. Photograph: Allstar/Cinetext/Orion Classics

Burley recalls that when he first started out, subtitles were stamped into the film stock using a wax and chemical bath method; the only way to correct typos would be to strike a new print. In the late 1980s, there was a huge leap forward with the first laser subtitling machines, which enabled video reviewing, allowing corrections to be made right up until the last minute.

Nowadays, clients provide translators with digital copies of the film, usually (but not always) with a transcript of the dialogue. Sometimes when the film reaches the subtitler, it has already been “spotted” by a subtitling lab, although the younger generation of subtitlers often do their own “spotting” – the technical process that fixes the entry and exit point for each subtitle and provides the character count for optimum legibility. “In a perfect world,” says Burley, “a subtitle will never go over a change of shot, but that is becoming increasingly difficult to avoid in today’s films, which are often more rapidly edited than older movies.”

The art of translation requires more than just fluency in several languages, and there is a lot more to it than simply translating the dialogue. “The subtitler must decide what to prioritise at any given moment, in order to best serve the interests of the film,” says David Buchanan, a freelance translator specialising in French to English subtitling, and a member of Subtle. “For instance, legibility. Is the subtitle clearly laid out? Does the text flow in a clear and logical way? Is the subtitle on screen long enough for the viewer to read it properly?”

Jacqueline Ball, a freelance translator specialising in German to English subtitling, says: “With subtitling, unlike text translation, you often have to make very difficult choices regarding what you can retain due to reading speed (which, on average, is 15 to 17 characters a second for adult viewers), how many characters fit on a line (usually between 37 and 42) and the number of lines – which, in foreign-language subtitling, as opposed to hard-of-hearing subtitling, is always limited to two.”

It’s also important for subtitles to take into account the characters’ ages, social class, personalities and moods, as well as the historical period in which a film is set. A knowledge of the plot is essential; when space is tight, you can’t cut dialogue about a gun if someone is going to be firing it in the third act. Other elements that must be taken into account are the rhythm of the language, as well as subtext. “The screenwriter has engineered all sorts of implications and resonances that work at a deeper level,” says Buchanan. “So a subtitler needs to be aware of the film’s underlying themes, symbolism, stakes and so on.”

Buchanan adds: “The act of subtitling lets you appreciate a film in a way that you would never get by simply watching it. You have to watch it at least three times, and you also have to empathise with every single character in order to effectively translate what they’re saying. So by the time you deliver your subtitles, you have already spent several days with these characters, getting to know them. You are so much more invested in it – as long as the film is a good one. If the film is substandard, then you are trapped in the company of these awful characters, and still forced to empathise with their terrible decisions!”

Linguistic variations in syntax, formality and grammatical gender pose their own problems. Ball cites the use of “Sie”, the polite German form of “you”, and the less formal “du”. “Germans will often ask each other, ‘Sollen wir uns duzen?’ [‘Shall we use the du form?’] which, of course, cannot be rendered literally into English. Usually you get round it by saying something like, ‘Shall we use first names?’”

‘Should we use the du form?’ Juliane Köhler and Bruno Ganz in Downfall. Photograph: Allstar/EOS/Sportsphoto Ltd./Allstar

It is also vital to have a knowledge of the culture you are translating from. “To a certain extent you are translating the culture as much as the dialogue,” says Buchanan. “For example, a UK audience might understand a reference to Asterix, but they would be less likely to understand an allusion to [the French TV comedy group] Les Nuls, or the inner workings of the French political system.”

As in many other disciplines, especially those connected to the arts, subtitlers are increasingly expected to do more work for less money, which inevitably takes its toll on quality. And while the shift to digital has made the craft easier, it has also thrown up new problems; modern technology enables film-makers to tinker with their films until the very last minute. “There is no denying that developments in software and the subtitling process allow us to achieve much better results,” says Burley. “The downside is that it goes hand-in-hand with tighter deadlines and more stress.”

Yet too many film-makers look on subtitling as an afterthought, an attitude the AVTE is seeking to correct. As Buchanan points out, “Subtitles are the conduit allowing you to communicate your film’s ideas around the globe. Bad subtitles can ruin millions of dollars’ worth of hard work. A film-maker wouldn’t outsource their colour correction or audio mix and just think: ‘I’ll leave them to it, I’m sure it’ll be fine.’ They would want to see it, hear it, get a second opinion, make sure everybody is on the same page. It should be the same with subtitles.”