be there just to make up the number/pretend to be an expert

滥竽充数

During the Warring States Period (475-221BC)， the King of the State of Qi was very fond of listening to yu ensembles. He often got together 300 yu players to form a grand music.

战国时，齐宣王喜欢听竽，通常是三百人的大合奏。

The king treated his musicians very well.

齐宣王给予乐师们非常优厚的待遇。

A man named Nanguo heard about that and he managed to become a member of the band， even though he was not good at playing the instrument at all.

所以有一个叫南郭的人尽管并不擅长吹竽，也设法混进了乐队。

Whenever the band played for the king， Nanguo just stood in the line and pretended to play. Nobody realized he was making no sound at all. As a result， he enjoyed his treatment just as the other musicians did.

当乐队演奏时，他就站在队伍里假装也在吹。没有人注意到其实他连一点声音也没吹出来，所以南郭也享受到和其他乐师一样的待遇。

When the king died， his son became the new ruler who also liked the music played on the yu. However， he preferred solos so that he ordered the musicians to play the yu one by one. Therefore， Nanguo had to run out of the palace.

齐宣王死后，他的儿子继承了王位。他也喜欢听竽，可是他喜欢听独奏，所以他让乐师一个个吹给他听，于是南郭不得不逃跑了。

The idiom “be there just to make up the number” is used to mock someone who pretend to be a specialist. You can also hear people saying it about themselves to show their modesty.

“滥竽充数”这个成语用来嘲笑那些没有真正才干，却混在行家里的人。人们有时也用“滥竽充数”来表示自谦。

其实“滥竽充数”的意思与“不懂装懂”是相近的，那在英语中就可以表达为“pretend to be an expert”，其中“pretend to be/do”的意思就是“假装是……”或者“假装做……”，而“expert”也就是“专家”的意思，所以“pretend to be an expert”也就是“假装自己是一个专家”的意思，那也就是“滥竽充数”啦~

有一本书的名字就叫做“Don‘t Pretend to be an Expert - Become One!”，那就可以翻译成“与其滥竽充数，不如学着吹芋”之类的。