their mistakes when they write in English

[navi tasan]

1) Their mistakes when they speak English are few and far in between, but their mistakes when they write in English are numerous.

Is that sentence correct?

 

[Piscean]

1) Their mistakes when they speak English are few and far in between, but their mistakes when they write in English are numerous.

Is that sentence correct?

Yes, if you delete 'in'.

 

[tedmc]

Why can't you make it simple:

Their spoken English is much better than their written English.