Troubles saving strings with special chars in MS SQL

The database is of a Windows ERP so I cannot save data in base64 or binary. In Windows I can successfully use special characters. In CodeIgniter the data returned by queries that contain special characters are displayed correctly, it is only when saving (INSERT or UPDATE) that the problem occurs.
I tried to update Raspbian (sudo apt-get update and sudo apt-get upgrade).
Unfortunately I'm not an expert programmer in php and unable to understand if there is any limitation or what I need to configure to solve the problem.
What can I do ?