Bilingual Tikiwiki-WordPress Migration

I’m moving an existing bilingual site (roughly 500 pages) from Tikiwiki v15 to WordPress and will run the new install with Polylang. All current forum content—threads, replies, attachments, user associations—must come across intact so that long-standing conversations remain searchable and linked to the correct users.

The visual theme can stay familiar; I only need light styling tweaks so the new WordPress front end feels modern without losing the recognisable look visitors know.

Tikiwiki’s granular user permissions are critical for us. I need an equivalent role and capability structure in WordPress, whether that’s achieved through native roles, User Role Editor, or a custom solution you propose. Everything else is fairly standard: menus, media, SEO metadata and friendly URLs should migrate cleanly.

Acceptance criteria
• All pages and forums imported, bilingual content correctly mapped in Polylang
• User roles replicated so each migrated account can access exactly what it could before—no more, no less
• Design matches current site with agreed-upon minor tweaks (colour, spacing, fonts)
• Thorough post-migration test plan completed: broken links, missing media, permission checks, forum usability, page speed

Please outline your preferred migration workflow (database export scripts, WP-CLI, custom importers, etc.) and an estimated timeline from kickoff to final QA sign-off.