The expression “so-so” is used to describe a situation that is “not so good, not so bad”.
This expression is so popular and well known among Japanese learners of English that it has become a part of everyday Japanese conversation. In fact, it seems Japanese speakers of English use this expression far more than native speakers.
If you want your English to sound more like a native-speaker’s try using the phrase “I guess” and “I suppose”.
How was the restaurant? “It was okay, I guess.” Was the movie good?” “It was alright, I suppose.”