Multivariant and multilingual wiki fixes and improvements

General goal

Most variant-dependent or language-dependent configuration variables/functions and the system messages using them should be supported for variants and languages.

{{SITENAME}}

Current

{{SITENAME}} = $wgSitename;

Suggested

{{SITENAME}} => {{int:sitetitle}}

Description

This both support multivariant site and multilingual site while {{SITENAME}} in various system messages should be in the language of message, especially in language variants.

$wgLogos

• T22807 Enable site logo displaying according to user language
• T273578 Wikis with language variants must override logo in Common.css
• T305692 Support language fallback for logo variants

wfMessage()

Current

wfMessage( 'message-key' );
wfMessage( 'message-key' )->inContentLanguage();
wfMessage( 'message-key' )->inLanguage( $lang );

Suggested

wfMessage( 'message-key' );
wfMessage( 'message-key' )->inContentLanguage();
wfMessage( 'message-key' )->inPageLanguage();
wfMessage( 'message-key' )->inPageViewLanguage();
wfMessage( 'message-key' )->inLanguage( $lang );

Description

(to do)

Translation:FULLPAGENAME/Page_display_title/*

Current

Translation:FULLPAGENAME/Page_display_title/*

FULLPAGENAME translation

Suggested

(to do)

Description

It should provide a way to fetch page display title without namespace translation. See Template:Localized_link in MediaWiki.org .