I am trying to prioritize what languages my software should be translated to. Regardless of other factors, I want to first look at how many people are native speakers of each language, example:
Punjabi: 102 million Wu: 80 million
PROBLEM: Most Wu speakers also speak Mandarin fluently, so translation is not such a priority. I suspect many Punjabi speakers are also fluent in Urdu, but I am not sure what proportion. I need to know that proportion, so that I can for instance prioritize Punjabi over Wu.
QUESTION: For each language: What is the second language of most of the speakers? What proportion of the group can be considered fluent in this second language?
Example (made up):
Punjabi: Urdu, 50% Wu: Mandarin, 98% German: English, 60% English: Spanish, 20% [...]
"Fluent" means being able to normally use a full-featured auctions mobile app in this language, or something similar of that level.
Context: While usually software localisation is prioritised more with regard to market considerations than with regard to actual numbers of speakers on Earth, my case is different. The software is open source, my only goal is education, I don't care about the users' per capita GDP. The software is designed for offline use, and runs on old/cheap phones, so network connectivity and technological advancement is not really an issue, at least not an issue that requires twisting the question.