Learn English – When someone can speak a language very well, they are “fluent”. What if you can only understand it

But is "I can listen to English" correct English?
Or should I say "I can hear English"?
Are there better ways to say that?

First up, "I can listen to English" is correct English. But you are trying to say that you can understand English that is said aloud. Just by saying "listen" doesn't necessarily mean that you understand spoken English. I can listen to Greek, but still not understand, because I don't know Greek.

Some better ways to say it are:

I can understand spoken English
I can comprehend spoken English
I can understand English that is spoken.
I can understand English that is said aloud.

Edit:

If understanding is not really necessary, just hearing and being able to listen to the language, you could try:

I can catch the English language most of the time.
I can make out spoken English.
I can take in spoken English

Presumably you want a word to describe a non-native or learner of the language. For Europeans learning other European languages (where the writing is in the Roman or Cyrillic alphabet and learning to read is trivial in comparison to speak and listen), you would say that a person has

having reading proficiency

in the language. For a single word adjective, I don't think there's a wod for any particular ability like 'speakability' or 'readability' (that means what you want it to mean).

For languages where the accepted writing system takes much more study like Chinese or Japanese, most people learn those languages academically where the proficiency in both go at about the same rate (it's almost like learning two different languages at the same time, spoken and written).

For the other side, for native speakers, there is only the issue of whether they can read their own language and for that

literate

captures the idea.

'Literate' could also work for the non-native learner, but even though intended for only the reading skill, might be misunderstood for 'well-educated' in the language, meaning both able to read -and- speak well.