Bug 7514 Choose OPAC language with URL parameter

Bug 7514 Choose OPAC language with URL parameter

Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Tested:
- with and without cookie set
- different language codes

http://.../cgi-bin/koha/opac-changelanguage.pl?language=de-DE
will directly open the German OPAC.

http://.../cgi-bin/koha/opac-changelanguage.pl?language=en
will directly open the English OPAC.

Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>
(cherry picked from commit 8ec812d97de321d8100f8e80ccad06cc36840e12)

Signed-off-by: Chris Nighswonger <chris.nighswonger@gmail.com>