Modify Catalyst API so it supports patchdemo's option to send a language code:

A language code can be configured using the local setting option wgLanguageCode. Files with locals settings options can be placed at dir settings.d under the wiki directory and they will be honored by MediaWiki. Alternatively, the value can be appended to the default LocalSettings.php (this is what patchdemo currently does)

Proposal

In the mediawikiCore section of the MW main chart, add a new value for the language code (default en).

Patchdemo will pass along the value as part of values.mediawikiCore and the MW chart will use it to configure the local settings.