Hi Boris:
Nice catch!
Keep in mind that players may face warning or penalty for any act that is opposed to the rules. I can hear TDA Founding Director Dave Lamb making this point. However, there is a distinction that some rules have required warning or penalty whereas other rules have optional penalty at TD discretion; see Rules 70 and 71.
But back to Rule 18-b, there's no stated requirement that the last aggressive hand must maintain his / her cards if they see themselves defeated at showdown. Case 1, aggressor sees defeat and tosses his cards towards the muck. No problem... if an opponent speaks up and says "I called and want to see that hand" it should be tabled, but there's no guarantee the cards won't hit the muck irretrievably first. Case 2, aggressor sees defeat while opponent speaks up "I called and want to see your hand". If the aggressor then attempts to hit the muck face down there's an argument for at least a warning at TDs discretion, especially if the dealer asks the aggressor to table. I probably wouldn't go to a penalty for first offense but it's at TDs discretion.
But if the French translation reads as you interpret, then that does seem over-stated. If it read "may be subject to penalty at TDs discretion" then it's reasonably consistent with implied warning or penalty as mentioned above.
This raises another question whether 18-b should have language to the effect that seeing the aggressors hand is not guaranteed. Caller can ask, but if in the circumstances the cards were previously mucked there's no guarantee of seeing them. Conversely we do say it is an "inalienable right to ask" so.... maybe best left as-is. Thoughts?