English: You cannot select two languages that have the same <a href="https://en.wikipedia.org/wiki/List_of_ISO_639-1_codes" target="_blank">iso code</a> but different formalities because doing so will lead to duplicate <a href="https://developers.google.com/search/docs/specialty/international/localized-versions" target="_blank">hreflang tags</a>.
Dutch: Je kunt geen twee talen selecteren die dezelfde <a href="https://en.wikipedia.org/wiki/List_of_ISO_639-1_codes" target="_blank">iso code</a> hebben maar verschillende formaliteiten, omdat dit leidt tot dubbele <a href="https://developers.google.com/search/docs/specialty/international/localized-versions" target="_blank">hreflang tags</a>.