What about the Arabic language? Christian Arabs also use the word "Allah" for God. There is no other word in Arabic for God. And Christian Arabs were using the word "Allah" before the Muslim Arabs since the Muslim religion only came into existance around 600 A.D.
I am aware that some Arab Christians, especially Melkite Greek Catholics, do indeed use the word "Allah," which is proper because it is part of their own liguistic tradition. However, the Catholics in question in Malaysia are of the Latin rite, and the use of the word Allah, in the liturgy is is not justifiable. The "Malay mass" is supposed to be in the Roman Rite, which should be celebrated in Latin. The word "Allah" has no historical justification to enable it to be used in any Roman liturgy, even if the liturgy could be translated into the vernacular.