It's not my strongest area of expertise, but the key thing that I do know for certain is that your database content and your database collation and your php file encoding and your html output need to all use the same encoding. If you start changing them in one place, you need to change them in all places.

THE MOST IMPORTANT thing you've said thus far is that "YESTERDAY IT WAS ALRIGHT and suddenly it changed". So, the IMPORTANT thing you need to do NOW is fix whatever you changed yesterday.