Perform missing steps for Catalan activation

This is about some of the steps documented in: https://tails.net/contribute/working_together/roles/translation_platform/operations/#index2h1

• Edit ikiwiki template files:
  • wiki/src/templates/news.tmpl and wiki/src/templates/page.tmpl may need some strings as 'Donate' that can be learned from the translation platform. → obsolete!
• Add .donate and locale bits to wiki/src/local.css → obsolete!
• Add the new language to wiki/src/contribute/l10n_tricks/language_statistics.sh
• Remove obsolete bits from translation platform operations doc

refs #20047 (closed)