How can I write another language than English on a GUI Text

Just type it in. Are you actually having any problems?

My problem that when i write with some languages (like Arabic) there is some problems like the characters is not attached the each other and the text is left to right and it should be right to left

OK, specifying Arabic was fairly important. That's a special case and Unity doesn't have any built-in support for it, but there may be something on the asset store which could help.