Germany and likely FRance won't....
If a tactical nuke is used, it will stun the world and freeze it in a moment of horror. I wouldn't put anything past what will be used as the escalation continues. This is war, and no nation is going to just forget about it's soldier's being slaughtered when it has the ability to stop that slaughter in an instant. Anyone ignoring this scenario has their heads up their aces big time. Two atomic bombs were dropped on major population centers in Japan during world war two, and it was to limit the amount of casualties overall, and to break the will of Japan to conduct war any longer, otherwise meaning that without those nukes a full scale invasion of the Japanese mainland was to become imminent in the situation, and that was unexceptable..
What part of Russia being a nuclear state does the world, and especially Ukraine not understand ??
All the drums of war being constantly beat upon is escalation not de-escalation, otherwise it would be best to find a more peaceful solution to the serious problem between these two countries instead of war mongering and flexing the muscles of war up untill a very tragic end for all the world to witness.
Convincing Ukraine that it is up against a foe that could obliterate them with a tactical nuke might be a way to stop the drums of war from beating on both sides, and to hopefully bring all sides back to the diplomatic table somehow.
It would not show a means of coward on Ukraine's part to understand this, but rather it would be a realization that they are actually dealing with a nuclear state that's only been held back thus far because of world sentiment over the issue, but if Russia begins to lose overwhelmingly in theater, then who knows what will be the result of that if it becomes desperate enough.
Time for the world power's to work towards de-escalation instead of escalating through this watching of a modern war as if it's a movie out of Hollywood.
Avoiding nuclear armed conflict anywhere in the world should be the work going forward.