chore: web/i18n todo

[mcdurdin]

Extracted from TODO.md, needs review.

Other tasks:

• PHP upgrade to 8.x
• localizing markdown files

Questions for url scheme:

• URL scheme - very little overlap with langtags (/cdn)
• How do we lay out files in the repo?
• How do we manage relative links?

keyman.com/windows --> has link to /linux

keyman.com/en/windows --> /en/linux
keyman.com/de/windows --> /de/linux

navigate to keyman.com/linux ->> keyman.com/de/linux (based on geography or by browser lang tag info, by default)

keyman.com/km/linux --> selects 'km' language, stays there.

Fallback?
keyman.com/de/windows --> if no fallback available, use en content, and maybe have a banner saying 'content not yet available in German, please help us translate this!'

• transition from existing links? must ensure we have redirections (e.g. /windows --> /en/windows)
• canonical links?
• links embedded in pages on keyman.com:
  • should be using relative rather than absolute links (i.e. ../windows rather than /windows)
  • Link types:
    • dynamic by Javascript
    • dynamic links from api.keyman.com data
    • dynamic by PHP script / static in HTML (91 .php files)
    • static in Markdown (39 files)
    • .htaccess redirects and rewrites (16 files)
• external links from other keyman.com sites
• external links from other sites --> should be handled by redirections

One plan:

• Move all content pages into a subfolder, including root index.php, e.g. '_content'. All folders except _common, _..., .github, .well-known, cdn, and go, (resources and others!) as a starting point.

• In the top-level .htaccess, split out redirects from markdown/php/file extension handling

• Add rewrites for all content pages, to, e.g.:

  1. redirect /windows -> //windows (initially, always redirect to /en/windows)
     This could be a static redirect map for the known pages (similar to # per-language landing pages in /.htaccess)
  2. rewrite //windows to /_content/windows?lang= --> redesigning the PHP and Markdown rewriting section of .htaccess to work with localization.

  PSEUDOCODE:

  Rewrite //...

  RewriteCond "$1" !-f
  RewriteCond "$1" !-d
  RewriteRule "^/([a-z][a-z])/(.+)$/" "/_content/$2?lang=$1" [??? include query string, last]

  Perhaps ([a-z][a-z]) should be a better quality match, e.g. exclude known strings such as cdn,web,go,...?

  3. rewrite for .md would embed the lang parameter and the appropriate _content path also.

• Fixup absolute links in _content/ files to relative links

• Fixup absolute links in header files to relative links (make a helper function?)