I have seen this issue many many times throughout my career so i thought it might be worth to go through it in details and help others.
If you have international content in your database and suddenly you see things like "é" or missing characters like "?" instead of "è" you may be in trouble. It is a symptom of lack of consistency in the ways you write, read and store unicode characters.
I hope my explanation, even that lengthy, will shed some light on the core of the problem and possible solutions :)
