Non-tonal music is written in a way that is not based on any particular musical key.

There are some non-tonal passages in the piece that are tricky for the singers. 这首音乐中有一些无调小节对歌手来说很难。

The composer would only work with classical pieces and eschewed anything non-tonal. 这个作曲家只会作经典作品而避开任何无调音乐。

A non-tonal language is one that does not use tones (= changes in how high or low the voice is that can change the meaning of a word).

Although some of the dialects are tonal, most are non-tonal. 虽然有些方言有音调，（但是）大部分的是无调性的。

If you are a native speaker of a non-tonal language like English, Chinese is particularly hard to learn. 如果你的母语是无调性语言，比如英语，（那么）汉语（对你来说）会特别难学。