Which do you think is freer and less stringent in terms of collocations, Arabic or English?

Sir It depends on many factors. Global English which has more American Influence is much simpler and less structured. Also it is much less formal. 

In British style you start a letter with Dear Sir. In Global/American u start with just Hi,. 

think both the Arabic and English languages are freer and less stringent in terms of collocations. Anyhow this depends on the people speaking a language and the rules that governs a particular language, knowing that such rules change and vary over the time, as part of an inevitable development of any language.

The answers to this question may  vary according to ones first language and/or preference.  Each language has its unique set of rules to follow so it's pretty much a case of comparing apples and oranges. From my perspective, I would say English, as this comes naturally to me. 

I agree with experts answers, thanks for the invitation. ..

 I feel The Arabic language

More liberal and more Arabic language tradition as they have their controls such as sections and are the oldest languages history

thanks for your invitation

i agree with mrs.maha's answer