Fix t/invalid_login.t failing without TEST_USER ENV variable
Use Catalyst::Plugin::Unicode::Encoding instead of deprecated Plugin::Unicode

Catalyst::Plugin::Unicode is deprecated and Catalyst::Plugin::Unicode::Encoding
should be used instead. The latter is in the Catalyst core since version 5.90040.
Since that version will autoload the plugin and issue a warning if it's still
in the plugin list, only add it on older versions.
Helpful error message if language configuration is missing

When the language configuration is missing (probably because we couldn't
find the configuration file) the user would get a screen full of error
message about Petal not finding a template. Improve this case by pointing
to the actual problem as soon as possible.