SEOptimerのHreflangチェッカーツールは、多言語サイトで推奨されるページ上の代替言語タグの存在を識別します。
Hreflang is an HTML attribute used to specify the language and geographical targeting of a page. It is commonly used together with the 'alternate' attribute in the code of a page to signal to Search Engines a list of alternative language or geographic versions of the current page.
If you have multiple versions of the same page in different languages, it is important to add Hreflang tags to tell Search Engines about these variations. This code may need to be manually added into the HTML code of your page, but is also often controlled by your CMS or plugin system if multi-lingual features are enabled.