Add ability to force language via url parameter

[ewinslow]

Could have sworn I already reported this... Oh well.

&lang=en should force English, for example. One way this comes majorly in handy is that it's easier to test other languages. Instead of changing your usersettings you can just change the url.

[cash]

Use the Developer tool plugin for this?

[ewinslow]

I think this should be core, actually.

[cash]

If this is about testing the site, it should be developer plugin.

[brettp]

There's a use case beyond testing the site. If you email links out to specific pages (like register) you can make sure the site is forced into the user's preferred language. The same could be accomplished with the browser's language prefs, but that's less reliable (users checking email on public browsers) than using a hard-coded language.