Technical SEO is most effective when it is considered during routing, data modeling and rendering. Later fixes are possible but usually more expensive.
Multilingual sites
Separate stable URLs per language, correct hreflang references and canonical URLs prevent unnecessary duplicate-content signals. Language switching should ideally lead to the corresponding translated page.
Rendering and performance
Search engines need reliable HTML content. SSR, SSG or properly generated static pages can help. At the same time, JavaScript, images and fonts should remain controlled.
Information architecture
Services, projects, products and specialist articles need clear hierarchy and internal linking. Good navigation supports search engines, but more importantly it helps users.
Migrations
During relaunches, redirects, existing URLs, sitemaps, canonicals and indexing rules are part of the migration. Visibility should not be lost through a technically clean but SEO-blind rebuild.