I can't get the achievement 'Sakoku Law'

[Trin Tragula]

Please bug report in the bug forum and include the save if you believe you are not getting the achievement when you should
Having the save is imperative to look into things like these.

Instead, it means you have to pick ONLY the options that increase your isolationism for the events that come from six incidents.

The achievement description should read "pick isolationist options only, for 6 incidents".

This is not correct. What it means is you have to get the isolationist outcome in the incidents, that does not necessarily mean that you pick the isolationist choice every time (though that is a sure way to get it).
All incidents have 3 possible outcomes, one open, one neutral and one isolationist. Which one you get depends on the total sum of your choices (as is indicated by the tooltips when you make those choices).

 

[Trin Tragula]

If you're going specifically for the achievement I would probably go with the most isolationist option in all events either way, just to be sure. Some events push the outcome more than others and while this is indicated in the tooltips when it is so it can be hard to predict before actually getting the event.

 

[neondt]

Thanks, I understand.

However, I still have a question. If i attained level 4 isolationism, the other events maybe not occur? because all doors are closed.

You still get the other incidents regardless of your level of isolationism.