The truth is that it makes no sense to comment in Spanish when the main content or topic is in English, it's a bit far-fetched. Just like the new trend I'm seeing about commenting in two languages. If you, as an English speaker, want to consume content in another language that you don't understand, you will surely use a translator, so use the same tool to comment if you want to contribute something, it's as simple as that. But well these are just my thoughts, I could be wrong, I'm sure I am.
I don't mind commenting on two languages as it means the commenter is of a different language and translating their comment to a different one for a broader audience and it's quite good, it shows they care. But when they don't give a damn and drop their comment on a language that is different from what I used, it's frustrating, so I'm going to ignore them from now on.