How to deal with turbulence while flying glider? (Cautions in applying rudder)
Everyone chooses what to worry about. I would not choose to worry about this.

Is such risk realistic in glider flying?

What does &quot;realistic&quot; mean to you?  If it means &quot;could it happen&quot; then sure, it could.  Plenty of things could happen.  If a possibility greater than zero is all it takes for you to worry then by all means, stop reading.  Don't forget your shark armor and anti-meteor hard hat when you go out next.
However, most people consider &quot;realistic&quot; to include likelihood. Is it likely? Well, I searched through the last 8 years(1) of the NTSB accident database for glider accidents involving the term &quot;breakup&quot;. Of the three relevant results, two involved aerobatics.  How many glider flights have there been in the last 8 years? Probably plenty of them.  Do you plan to do aerobatics?  If not, then your accident statistics are one in plenty.  Only you can decide if that's too scary for you.
It is not on the NTSB 10 most wanted list.  I have not read about it in FAA Safety Briefings.
In my experience, new students don't know what is important, so as a proxy, they worry about things that are vivid.  In-flight structural failures that have videos made about them are highly vivid.  That's why my original answer started out by saying &quot;this is not a valuable use of your attention&quot;.  If I were your instructor, I would advise you to focus your concerns on flying proficiently and learning good decision making.  If you do that, the concerns here will take care of themselves.

If one encounters air turbulence in while flying glider, how to deal with it, and what to avoid?

There is no &quot;if&quot; here.  You are definitely going to encounter air turbulence. That's how you know you're doing it right.
How to deal with it? Pay attention to your instructor, monitor your attitude, remain calm, and fly the aircraft.

(1) - Why 8 years?  Because I got bored.