The following should make it possible to enter accented/marked characters directly from the keyboard, rather than having to look them up in a character map:
- In your desktop manager's control panel, there should be a "keyboard preferences" control - open that.
- Somewhere in there should be a "keyboard layout" section, probably a tab. Go there.
- You'll want to find where to set the "compose key". In MATE, this is reached via the "Options..." button.
- Set the "compose key" to be whatever key works best for you. (I use the left [Windows icon] key.)
- Save changes.
- You should be able to enter accented characters by pressing [compose] followed by a key-pair, e.g. [compose][e]['] = é
I should put together a guide for the less-obvious diacritics... e.g. you'd think ü would be [compose][u][:], but actually it's [compose][u]["].