I have that exact same problem when I was watching Kuuga. But I also learned that those sub-titles were not included in the original air of Kuuga as the director wanted to present the grongi as mysterious beings. It's frustrating sometimes for me. I think the subs were only added on the DVD release later on. So if you are seeing those subs, you got lucky. Unless you can speak grongi. Did you know they actually constructed the grongi language? It's similar to japanese in grammar but uses different sullables.