How relevant do you think knowledge of a product is in Retail? Can a human resource from a different product background be employed?

Procuct knowledge is acquired by experience and trainings. 

If the Human Resource's goal is to hire competitive and highly qualified individual then they should not hire someone who is not relevant for the position, as the company is not a training ground.

If the Human Resource's goal get someone with less qualification who will accept less salary they they could hire someone with no relevant experience and spend time and money on trainings.

Sure why not, if they have through knowledge and confident.

How to handle the product in global market only they must know the language of business 

On other side Only good working expereince in reserach and development