From OpenOffice Download Page what Open-office version should I download for Ubuntu 11.04 Desktop AMD64, that has English interface and supports Arabic characters?
To download and install Open Office for Ubuntu 11.04 am64 you need a Debian package (DEB) file compiled for this 64-bit architecture (named Linux x86-64 DEB):
Download with this link for the arabic localization.
However consider this:
By adding a repository or ppa and installing from there you will automatically get the proper version in addition with regular updates. This would be the recommended way.
To support arabic writing in an otherwise English language locale of Libre Office install language-support-writing-ar