An hreflang tag is a small piece of code that tells search engines which language and regional version of a page belongs to which audience. When you have the same page in English, Dutch and German, hreflang is how you say “show the Dutch one to Dutch searchers and the German one to Germans.”
Imagine a museum with signs at every entrance pointing speakers of each language to the right tour. Without those signs, visitors wander into a tour they cannot follow; with them, everyone is routed to the version made for them. The tags usually sit in the HTML head of each page, and every language version references all the others, so search engines reading them during crawling see a complete, consistent map. You can monitor whether they are working in Google Search Console, which flags mismatches.
The most common mistake is incomplete linking. If the Dutch page points to the English one but not the reverse, search engines distrust the whole set and may ignore it, so the references have to be mutual.
The value codes trip people up too. The language part uses ISO 639-1, so “en” or “nl”, and the optional region uses ISO 3166-1, so “en-GB” differs from “en-US”. A frequent error is writing the region as a language, like “en-UK”, which is invalid and silently dropped. There is also a special value, x-default, that names the fallback page for any visitor your other tags do not cover. Get those codes right and the rest is mechanical.
At TopDevs we set up hreflang properly on every multilingual site we build, so the right audience reaches the right page without the wrong-language detour.
