Yes, English is the "universal" language, whether we like it or not, and speaking in another language in a public place (such as a github issue tracker) is disrespectful, because it's like gatekeeping information and knowledge.
No it's not. This is imperialist thinking. There is no universal language.
If you want to understand what they're saying hire a translator or use an online service. They're not using some obscure language only a few people understand.