From what I can tell I have to have the entire Gmail interface in hebrew to switch my input language to hebrew.
If I type in hebrew with US English set as the display language: 1) I can’t spell check in hebrew, 2) I can’t change alignment (hebrew is right to left, unlike english which is left to right).
Anyways, its rather cool that they’ve added hebrew spell check, etc. I’ll have to keep playing with this.