As a potential user of an open source project, I care a fair bit what language it is implemented in. As an open source project, I preffer projects in languages and ecosystems I am familair and comfortable with. I may need to fix bugs, add features, or otherwise make contributions back to the project, and thus I am more likely to pick a solution in a language I am comfortable with than in a language I am not as comfortable with, given my other needs and priorities are met.