Why non-Muslims over there, who I assume don't speak Arabic, have chosen to use the word is unclear; but they have, and the Muslim majority don't like it. So much so, the government banned it, then the ban was overturned, then it was banned again, and when Christians appealed the decision, the courts just upheld that ban.
It's been an ongoing battle for quite some years.
The first time the High Court overturned the ban in 2010 was after a Roman Catholic newspaper- The Herald- petitioned to be allowed to use Allah in its Malay language editions. In what has become a common overreaction by Muslim hardliners to minor things they find offensive, 9 churches were firebombed. The attacks were a blow to the government's "1Malaysia" credo, with its major focus on ethnic and religious harmony. Though it's obviously not such a great concern.
Christians believe it violates their religious rights not to be allowed to use 'Allah' since the word has somehow made its way into the Malay language, but Muslims are usually only concerned when they believe their rights have been violated, so they don't really care about anyone else's. The typically paranoid reasoning behind the controversy is the fear of proselytizing. Yes, apparently the Malaysian government is afraid that if everyone uses the word, Muslims might become confused and might unwittingly be converted to another faith. It's some nefarious plot by Christians to gain converts, which of course it's not.
According to Judge Mohamed Apandi Ali:
... the use of ''Allah'' was ''not an integral part of the faith and practice of Christianity.'' ''It is our judgment that there is no infringement of any constitutional rights'' in the ban, he said. ''We could find no reason why the (Catholic newspaper) is so adamant to use the word 'Allah' in their weekly. Such usage if allowed will inevitably cause confusion within the community.''
Words are words and they don't belong to anyone.
The editor of The Herald, Rev. Lawrence Andrew, plans on appealing- again.