Gingerbread DOES have support for Arabic. I've used it on my phone. However each supported language comes with files and such that need to be downloaded and installed. Each ROM is doing to be bundled with different language packs by default depending on where they expect the ROM to be used. If your ROM is from a country specific carrier, don't expect many languages!
The ROM I use comes in four flavors with about 25 languages each, and you download the version that has the languages you care to use. I use the one that has middle-east languages rather than the one that has eastern European ones for example.