I’m also using GeneratePress, and creating sites mainly in Finnish. I find it very slow to work in the customizer, if it’s in Finnish, because I’m always looking for English terms, such as “Footer” or “Widgets”, instead of their rather silly translations. Having the admin consistently in English is much easier. I use Mac OS in English too, because of consistency and terminology. Also, it’s easier to find help online, when you don’t have to translate the words before searching. I would like to have the option of using GeneratePress admin in English, regardless of site language. It would be better to have this option within GeneratePress, because a third party plugin will most probably not have the option to select translations for theme settings or plugins separately. Content administrators (editors) usually like to work in their native language (in my case, Finnish), but the developers tend to prefer English. I know a lot of Finnish WordPress developers, and they all like to work in English.