Problem with symbols !!!

Hello,
I am building a website with wordpress.org
Because of the specifics of the content there is a lot of symbols like “è”. Insert is not a problem, but the prolem comes after click on “Update” – the symbol turns to “?” (exmp: Bèlla, becomes B?lla). There is a solution in case there is only one symbol in the content of the post or page – you have to go to HTML tab and insert symbol with its HTML code &engrave;.
Unfortunately if you have to insert another symbol like this one and you do the same steps , the first changed one again turns to “?”.

Does anyone has an idea how to deal with this problem, because for me it is a very big problem … i have a lot of symbols in the content!

Thank you in advance!