I think this only effects ToDos that are in status "Planned". You cannot have planned ToDos in the past. Change the status to something else and you should be able to modify the record however you want. In fact, I think the message says "in status planned cannot be in the past"
Is possible that you added the value "Planejado" and now you have in database the value "Planned" and "Planejado"?
If you have this , you see the duplicate values, because are differents, one is translated and the other not.
You can check this on your database , table vtiger_eventstatus
But if only that, when editing system will exhibit this new lines, and I could delete a duplicate value, I think ...
In this case, I should remove, thats duplicate lines, directly in DB? I need change another table or do another changes ? I means, simplify remove thats lines in DB not causes any problem?
You can remove this value directly from database on table vtiger_eventstatus , but maybe you can have some records with "Planned" value another with "Planejado".
So I think that the better option is change user user admin to english, got to settings -> picklist editor and try to remove the value Planejado, when you do this I remember that ask you if you want to replace this valuer for other on the records that have assign Planejado value. If yes, you can indicate that you want Planned and elimante Planejado.