I want to make a website in both languages Arabic and English, in the way that I can change from Arabic to English from the upper menu. I want to make it as word-press based website and buy a theme to use it and base my website upon it. note that arabic is written from Right to left, so we have to take this into consideration as well. is there a possibility for that and how it can be done. if there any plugin I can do?
If your site has the same content in both languages, you may try the plugin I have written called Transposh, which allows you to handle this with ease.
Support for RTL languages is embedded, where the theme has support for this. On the default themes it works quite well.
If you have different content for different languages, there are other plugins to try, and the multisite route is also quite notable.