In multilingual SEO two things have to be right: every language version has its own address, and the versions tell search engines about each other with hreflang. Everything else is ordinary good SEO, done separately in each language.
Language or country?
Decide first whether you are targeting a language or a country. An English page for everyone who reads English is different from separate pages for the UK and the US. For most companies, language is enough.
An address of its own for every language
A language version needs its own permanent address, for example a subfolder: example.com/fi/. Do not switch language by cookie or browser language at the same address, because Google then sees only one version.
Do not redirect visitors automatically to another language version either. Offer a visible language switcher and let people choose.
Hreflang says which pages belong together
Hreflang tells Google that two pages are language versions of the same content. Three rules cover most of the mistakes:
- The tag must go both ways: Finnish points to English and English to Finnish.
- Every page also points to itself.
- The addresses must be exactly the ones that are indexed.
The canonical points to its own language
Each language version’s canonical points to the page itself, not to another language. If the English page’s canonical points to the Finnish one, you are asking Google to leave the English out.
Translation is not enough: localize
People search differently in different languages. A direct translation rarely lands on the word that is actually used.
Do keyword research separately for each language and write the headings accordingly. Check the examples, prices and contact details as well.
Check these in WordPress
A translation plugin usually handles hreflang correctly, as long as every page is linked to its translation. Check that the sitemap includes every language and that the language-specific homepages work.
More on language versions in WordPress: WordPress SEO. Wider checks belong to technical SEO.