One more clue: if I create a new doc the problem disappear. But if I export to idml an old document in russian the problem persist...
What dictionary is applied to Russian in InDesign's preferences dialog for the Russian Language (not in the Para Style).
Do the documents where it works have the same settings?
You show up with an Italian Language Settings Screenshot. But for your problem the Russian setting would be important. Maybe that you might change the language module for Russian or maybe that it has changed.
I think the problem is inside the file because the settings in the old file and the new file are exactly the same!
And before the trash of the preferences all the dictionaries (all the languages) work perfectly! =(
I think there's something corrupted in the file that the simple export to idml doesn't fix! =(
Anyway I've tried change the language you see in the screenshot from Italian to Russian but nothing changes!
I've trashed again the preferences and export again the idml... nothing changes!
I'm thinking of re-install the entire program but this solution is very time consuming.
Please, can anybody give me some advice?
I've always had this problem with Russian texts and I finally found a solution. All I needed to do was to change the setting of Spelling for the Russian language under Preferences>Dictionary. I can switch back to the previously selected dictionary and it will still work, must be a bug.
Hope it works for you too.