Does it sound strange?
"I have to bone up on English as I want to pass this exam with flying colours"

I just wonder if 'bone up on' is used in this context. Or it's better to say "cram"

Thank you for your answer!

Question

Does it sound strange?
"I have to bone up on English as I want to pass this exam with flying colours"

I just wonder if 'bone up on' is used in this context. Or it's better to say "cram"

Thank you for your answer!

Answer

Hi! To answer your question, I don't think I've every heard "bone up" as an expression before and cannot see myself ever using it, so I would definitely use "cram" instead. Perhaps it is a regional expression?

Answer

"bone up" is perfectly correct.  You can find examples of its use here:  http://idioms.thefreedictionary.com/bone+up

"cram" is to study something intensively at the last moment, for example, just before a test: http://idioms.thefreedictionary.com/cram

Answer

They are not exactly synonymous. 
Cram - suggests last minute preparation
Bone up - more considered and planned learning