Thanks for the answer.
The characters I want to use are there, but when I use them a rectangle
appears where the character should be :(
I'm using the strings.xml to put the buttons text, like this:
and in the layout XML file I reference this text like this
<Button android:text="@string/arrow" ... />
I'm I doing something wrong? I suppose I'm not, because this method work
very well with the other characters.