How do you say in traditional Chinese : do you play an instrument?

"Traditional Chinese" is not a language; it's a slightly different set of written characters from "simplified Chinese characters."

If you want to "say" something in a Chinese language, you could say it in "Mandarin" (putonghua), Cantonese, or any of several other modern dialects, or in Classical Chinese (a language that was used for official, scholarly, and literary writing until the end of the imperial regime).

1. I think I understand your question. But before I know what kinds of instrument he plays, I am really in a hard situation to translate the simple English sentence into Chinese and Chinese Pinyin properly.
Because, in English you say “play cello(violin)”, we say “拉 - la”
cello(violin).
In English you say “play guitar(banjo)”, we say “彈 - tan” guitar(banjo).
In English you say “play drum”, we say “打 - da” drum.
In English you say “play trumpet (saxophone, trombone)”, we say
“吹 – chui ” trumpet (saxophone, trombone)
2. But anyway, I try to translate your sentence as follows.
你平常是否玩樂器?
Pinyin : ni　ping　chang　shi　fou　wan　yue　qi?
Wade-Gilos: ni　p'ing　ch'ang　shih　fou wan yueh　ch'i?
3.Now you can see the reason, why the above translation is a causal way of speaking.