diacritics not displaying

I just started using the polylang plugin in order to make a translation to my website.

When I write in the editor to create a post the letters display correctly. After I click publish / or update the text displays ? instead of ă ș and ț. The diacritics î and â display fine after saving but ă ș ț display as ? instead.
I noticed that words in the menu and theme admin display the letter ă correctly.

I tried updating the database charset etc. but no results. I use Twenty Twelve for this site.
I am told that I need to add a subset to open sans in the theme. How could I do this? I am writing romanian.

Any help is appreciated…