I agree with Bhavesh and Richard in that assuming what you really want is the user's session language and not the value from the user table or elsewhere.
The link Bhavesh posted to GlideUser (g user) - ServiceNow Wiki actually uses session language as an example so you can use a combination of Server-side (maybe a display BR) and client-side to get the data. g_scratchpad is also another option for passing to the client.
