Question

In a wikipedia’s article text, a link might be mentioned like: [Category:A B C], however the exact wiki url will have suffix like Category:A_B_C
From where I can get the information regarding all these rules which wiki uses to get the url from a link in its text ?(, e.g. converting spaces to underscores, capitalizing first letter, dealing with non-ascii characters etc)

Answer 1

Roughly the following:

• Normalize namespace, e.g. category: –> Category:.
• Uppercase the first letter of title proper, e.g. Category:foo –> Category:Foo. Note: this depends on wiki settings and titles are never uppercased on Wiktionary, for example.
• Replace spaces with underscores, e.g. Foo bar –> Foo_bar.
• Percent-encode all the usual characters with PHP’s standard function urlencode(), except for the following ones: ;:@$!*(),/.

For full technical details you could look up this (function getLocalUrl()) and this (function wfUrlencode()).