WordPress Theme Migration + Multilingual SEO Cleanup (WPBakery / Polylang / Rank Math)

I run a live bilingual (English/French) WordPress website for my moving company. Over the past several months, my local Google visibility has declined, and I am looking for an experienced WordPress developer who specializes in WPBakery, Polylang, Rank Math, and technical SEO to help stabilize and modernize the site. Current Environment WordPress Core: Fully updated Rank Math: Fully updated Polylang: Fully updated WPBakery Page Builder: Official standalone licensed version (not bundled with the theme) Hosting: HostGator with staging functionality available The only major legacy component remaining is my approximately 15-year-old child theme. Important Goal I do not want a redesign or visual refresh. The website should look and function exactly as it does today. My goal is to modernize the backend, improve performance and PHP compatibility, and resolve multilingual indexing issues while preserving the existing layouts and SEO value. All work must be performed on a staging site and only deployed to production once fully tested. Phase 1 – Theme Migration & Infrastructure I would like the legacy child theme replaced with a modern lightweight alternative (Astra, GeneratePress, or another suitable recommendation) while preserving the existing WPBakery layouts. Objectives include: Create and work exclusively on a staging copy. Migrate from the legacy child theme to a modern lightweight theme. Preserve the existing visual appearance and page layouts. Preserve WPBakery functionality. Recreate the existing header, navigation and footer if necessary. Improve frontend performance and compatibility with current PHP versions. Verify that WordPress core hooks (including wp_head) function correctly after migration. Complete deployment with minimal or zero downtime. Phase 2 – Multilingual SEO Audit & Repair After the infrastructure is stable, I need a thorough audit and cleanup of multilingual SEO issues. Current observations include: hreflang tags are missing from the page source. Google occasionally displays English pages with French snippets or French pages with English titles or descriptions. Previously removed URLs are still appearing in search results. XML sitemap generation needs to be reviewed and verified. Some French placeholder blog posts intentionally contain English content because they have not yet been translated. Some pages have duplicate -2 slugs that should be evaluated. Translation relationships between English and French content should be audited. Canonical tags and hreflang relationships should be reviewed together to ensure they are not sending conflicting signals. Appropriate redirects should be implemented for obsolete content where necessary. Pages intentionally left untranslated should be handled in a way that avoids confusing search engines while preserving future translation workflows. Expectations I am looking for someone who can diagnose the actual root causes rather than simply replace plugins or make assumptions. If you believe certain symptoms are caused by the legacy theme, please explain why. If you identify separate database, Polylang, or indexing issues, I would like those documented and corrected using the safest possible approach. Protecting existing SEO value throughout the migration is extremely important. When responding, please include: Your experience with WPBakery migrations. Your experience with Polylang and Rank Math. Whether you have handled multilingual indexing issues similar to this before. Your proposed approach. Your estimated timeline. Your estimated cost. I am prepared to hire the right expert immediately for a careful, staged implementation.