Liam is NOT an Irish short form of William. Liam is a short form of Uilliam, which actually is the Irish translation of William. My great-grandfather was named Uilliam by his parents (1894) and his mother called him Liam. I wouldn't say Liam is exactly trendy, but it's certainly not as rare as it once was. For the record, Liam hasn't been around for centuries. Uilliam probably has been though and even I know William has been.
For the record, Liam hasn't been around for centuries. Uilliam probably has been though and even I know William has been.