A spelling system can be described as non-phonetic if you cannot always understand how words are pronounced simply by looking at their spelling.

The non-phonetic nature of English can made it a hard language to learn. 英语的非表音本质使得它成为一种难学的语言。

He was struggling to master the difficulties of the non-phonetic spelling system. 他难以克服非表音拼写系统（带来）的困难。