OUSMANE sweats under a tin roof as he thumbs through a Chinese smartphone that he is selling at the technology market in Bamako, Mali. Words in French, Mali’s official language, scroll down the screen. “A ka nyi?” (Is it good?) a customer asks him in Bambara, Mali’s most widely used tongue.

Mozilla, the foundation behind Firefox, an open-source web browser, wants Ousmane’s customers to have the option of a device that speaks their language. Smartphones with its operating system (OS) are already on sale in 24 countries, including Bangladesh, India and Mexico, for as little as $33. Other countries will be added as it makes more deals with handset manufacturers. And Bambara is one of dozens of languages into which volunteer “localisers” are translating the OS.

Mozilla has 230 localisation teams, says Jeff Beatty, who co-ordinates some from his office in Utah. Their work takes both time and ingenuity. Firefox for a computer uses about 40,000 words; for the phone OS, 16,000. Translators must express technological terms in languages shaped by livestock, farming and fishing, and choose alternatives for culture-specific words such as “cookie”, “file” and “mouse”.

Ibrahima Sarr, a Senegalese coder, led the translation of Firefox into Fulah, which is spoken by 20m people from Senegal to Nigeria. “Crash” became hookii (a cow falling over but not dying); “timeout” became a honaama (your fish has got away). “Aspect ratio” became jeendondiral, a rebuke from elders when a fishing net is wrongly woven. In Malawi’s Chichewa language, which has 10m speakers, “cached pages” became mfutso wa tsamba, or bits of leftover food. The windowless houses of the 440,000 speakers of Zapotec, a family of indigenous languages in Mexico, meant that computer “windows” became “eyes”.

The world speaks nearly 7,000 languages. Mali, with a population of 15m, has 13 national languages and 40-60 smaller ones, depending on where the border between language and dialect is drawn. Firefox is available in 90 languages, which serve almost all of the 40% of the global population already online. Apple’s most recent computer OS offers 33 languages out of the box, and the new iPhone, 35. Google offers 150, including dialects (and some spurious ones such as “Pirate”). But some languages spoken by millions are excluded, including Tibetan (3m-4m speakers) and Bambara (10m, including those for whom it is a second tongue). Bringing the rest of the world online is not just a technical challenge, but a linguistic one.

As a non-profit, Mozilla can put effort into languages that offer no prospect of a quick return. Songhai and Fulah, recently made available in Firefox, are spoken mainly by poor, illiterate herders and farmers in the Sahel, who do not have smartphones. But when such people eventually get online, they will benefit more if they can do so in their own tongues.

As more languages are added, the Firefox OS will create a sort of global Rosetta stone. It uses all parts of speech, and older, colourful words are pressed into service. Mozilla has created a statistical tool for linguistic analyses. And though 40,000 words is not a whole vocabulary, it is a significant part. As well as bringing the linguistically excluded online, localisation may keep small languages alive.

Correction: This article originally included Indonesia in the list of countries where smartphones with Mozilla's new operating system is on sale. In fact it is not yet available there.