Lugamun has ten source language: Arabic, English, French, Hindustani (Hindi/Urdu), Indonesian/Malay, Japanese, Mandarin Chinese, Russian, Spanish, and Swahili. Five of these languages belong to the Indo-European family, the language family that has by far the highest number of speakers (it’s spoken by about 40% of the world population). The other five represent five other particularly widely spoken language families.

The exact method for selecting these languages was as follows:

• For the Indo-European languages – by far the most widely spoken language family in the world – we select the biggest language from each subfamily (or branch), provided that that language has at least 100 (or 50, it doesn’t really matter) million speakers. This results in four source languages: English (Germanic branch), Hindustani (Hindi/Urdu, Indo-Iranian branch), Spanish (Italic branch), and Russian (Balto-Slavic branch).
• For each of the four next biggest language families (all of which have more than 300 million speakers in total), we use the most widely spoken language: Mandarin Chinese (Sino-Tibetan family), Swahili (Niger-Congo family), Standard Arabic (Afroasiatic family), and Indonesian (Austronesian family).
• We also add French (the second most widely spoken Italic language), since it is one of the official languages of the United Nations – the only official language not yet in our list. French vies with Bengali in being the most widely spoken language not yet in our list – but it is arguably more international, being an official language in more than 30 countries (the second highest number after English), while Bengali is official only in Bangladesh and parts of India.
• To avoid having more Indo-European than other languages and to increase diversity, we also add the most widely spoken language from a family not yet represented: Japanese (Japonic family).

This choice was made in July 2021.

Sources:

• Ethnologue: What are the largest language families?
• Reddit: The world's 30 most widely spoken languages (Mar 2021)
• Wikipedia: List of language families
• Wikipedia: List of languages by the number of countries in which they are recognized as an official language
• Wikipedia articles on language families and individual languages
• Worldometer: Current World Population

Because most linguists do so. Hindi and Urdu are listed as separate languages in the dictionary because they use different writing systems, but that doesn’t mean they should be treated as different languages for the purposes of generating candidate words – rather, doing so would just yield identical duplicate candidates for nearly all words. It would be similar to considering American English and British English or Brazilian Portuguese and Portuguese Portuguese as different languages – yes, there are differences, but they are so small that it makes more sense to consider them as variants of the same language rather than as different languages.