言ってること理解できるけど、英語で返事をするのは難しいって英語でなんて言うの？

Both sentences here mean that you can understand when people speak in English but have difficulty when responding back in English

"Understand better than I can speak it." Means you can understand what they say but find it difficult to reply. "easier to understand than speaking it." also means you can understand what they say but find it difficult to reply. "I find it difficult to express myself in English." means you find it hard to explain what you want to say in English.

1. I understand what you are saying, but I find it difficult to express what I want to say in English. The phrase "difficult to express what I want to say in English" means that it is not easy to say what I want to say in English.

This is quite normal and not something to worry about. When a baby learns a first language it spends almost a year before feeling confident enough to try its first words!

"I understand you, I'm just struggling to find the right words to reply" is a saying you could use in a specific conversation where you are "struggling"- (finding it difficult) to say way you feel or really want to. "I understand english better than I can express myself in english" Is a more general statement you can say about your english skills over all. You understand better than "express" (say what you feel or think) in english.

Sometimes it can be difficult to respond to what someone is saying to you, especially if you are not conversant with the English language. Even native English speakers have to use the correct words and expressions. One cannot just respond haphazardly without logically arranging one's sentences. So, in your case, the problem is finding the correct vocabulary or expressions and sentence construction. So, you may say: I understand what you are saying but I can't find the right words to respond. or I do understand what you are saying but I am trying to find the correct way to say what I wan to say to you.

By saying “I’m better at.... than...” you can express that you are able to understand more than you can speak. Ex: A: I can understand English, but it’s hard for me to respond. B: I totally understand what you mean! -I’m better at understanding English than speaking it.

If we can understand or 'comprehend' what someone is saying to us, it means our English listening skills are very good. If we find it hard to express what we want to say back, it means our English speaking skills need some work. We can say that we find it difficult to think of a reply or that we cannot 'articulate' an answer. 'Articulate' is a verb meaning to say something clearly and fluently.

I understand, but I don't know how to reply. It is a simple way to answer, and people will understand. I understand, but I can't say what I want to say in English. The same, simple, and to the point.

It's a very common situation when a person knows English enough to understand but have difficulties explaining his thoughts to others. The second sentence I wrote is more detailed and I would prefer to use it compared to the first one, although, they both mean the same.

Sometimes we can understand a language much better than we can express ourselves. This often happens as we are learning a new language. When you are speaking with someone you can always explain that - "I understand what you are saying, but don't have the words in English to reply." "I don't know the words to respond in English."