Actaea

Which language is the international (Acteian) language?

But does it necessarily have to be a real language for the setting?
You could use a non-existent Acteian language.
Of the real ones, I would prefer Swahili.

What does "coerce" mean? The Steelmen are not part of the first Security Council. They are told: stop developing chemical weapons. The Steelmen's response (I'm omitting or replacing the profanity): "What? Who are you?" They are told: "We are the Security Council, and we have decided that the countries of Actea must..." The response: "We don't care at all; we are not part of your Security Council. Tell your wife how to cook borscht." "But what about security, blah blah blah?" "Go to hell!"

Everything you said is called "asking," not "coercing."
I'm talking about an economic blockade, a complete ban on the import of high technologies, weapons, and other things. Unlike Cuba, which had the USSR, and North Korea, which has China, this pressure could have a greater effect.
Of course, one could argue that these methods will only work against a state that has something to lose. But it is certain that not all natural resources are available in sufficient quantities, and not all technologies are advanced. And besides the economy, there is also politics, culture, and sports. At the very least, there is a reason to think about it.