Try to Have the Fewest Internationalised Versions of a Site
Adding many internationalised versions of a website increases the complexity, so you’re better to have fewer versions if possible, especially if you have pages where you can rely on geo-targeting without hreflang. You can use Search Console and web analytics to see if people are landing on the wrong pages, and implement hreflang for those. For different language versions, hreflang can help Google to show the right version, but searches for long tail content are easily recognisable for which language version to show, so hreflang may not be necessary.
Individual Hreflang Links to Non-working Pages Won’t Affect Other Links
Google will ignore hreflang links to redirecting, non-indexable and non-reciprocating pages, but this won’t affect other hreflang links.
Google Has no Mechanism to Prevent a Site Appearing in Specific Countries
Google will rank sites on a country code top level domain to a global audience where it thinks it’s relevant, and there is no mechanism to prevent this.
Duplicated Same Language Content for Different Countries May Not be Indexed but Can Show in Search Results
If you have same language content for different countries, Google will see them as duplicated and fold them together for indexing, but unfold them in search results.
Use Hreflang on More Generic Pages to Deduplicate SERPs
For a more generic query like a brand name, it can be hard for Google to understand which language version a user is looking for. Hreflang tags can help here to swap out incorrect language versions by using the user’s language settings.
Some Machine-translated Content Can be High Enough Quality to be Indexed
Machine-translated content is getting more sophisticated and producing better results, so if these pages are translated to a high enough quality then they are fine to be indexed. However, the translation results should be checked by humans to ensure accuracy and quality, which can be difficult to scale across a large number of translated pages.
Having Hreflang in Sitemaps vs on Page Makes No Difference to Google
It makes no difference to Google if you choose to include your hreflang configuration in an XML sitemap or on the page itself in the head tag.
Use Translation Tools Together with Manual Translation Reviews to Create a Localised Version of A Site
John recommends against using just Google Translate or other translation tools to automatically translate the content of a website to another language, as it is likely to be considered automatically generated content. Instead, he recommends using it together with manual translation reviews in order to create a localised version, which will also improve user experience and provide more valuable content to local speakers.
Keep One Version For Image File Names Rather Than Having Multiple Translated Versions
John recommends against creating translated file names for images and instead keeping one version. Image file name is used as a small ranking signal, but the text on the page it appears on is a much stronger signal.