How do I write with diacritics in Ubuntu Mate 17.10 Beta 1?

, I installed Ubuntu Mate 17.10 Beta 1, in Romanian.
How do I type with diacritic on the keyboard?

Salut. To enable diacritics for any language from what i know is that you need to press first Right Alt and hold it and then the key you want. Test it and let me know. Have a nice day. Sa ai o zi minunata. Cu stima APolihron

So I did and do Ubuntu and go, but at Mate 17.10 not!