I don't know if php and gettext is better than a javascript solution. For both solutions, i think that it needs change the code. If nobody tries we don't know what solution is better.
For a javascript solution I talked with friends, they tell me that they use "i18next" framework and there are plugins for php and jQuery. I told jQuery because AdminLTE has this framework.
I don't have any problem to try any solutions, new ideas or start another solution.