A bilingual website is a manageable thing: two versions, one person who reads both, and a mental model of what exists. At three or four languages that model breaks, and everything that was implicit has to become explicit. The structure, the tags and the record all matter from the third locale, and the sites that handle it well are the ones that decided those three before they added it.
What changes between two languages and four
With two, somebody knows which pages exist in both. With four, nobody does. The number of page-locale pairs grows with every language, the number of hreflang links grows faster, and the chance that any given page is current in every version falls sharply. The work does not become harder; it becomes impossible to hold in a head, which is a different problem.
The structures that hold up
A subdirectory per locale on one domain is the default for most companies: one domain's authority, one analytics property, one deploy. Country domains suit businesses with genuinely separate operations per market. Subdomains sit awkwardly between the two. What matters more than the choice is that it is made once and applied everywhere.
What to copy from sites that do it well
Three things, visible from outside: a language switcher that keeps you on the page you were reading rather than dumping you on a home page, URLs where the locale is obvious to a human, and no automatic redirect that overrides a deliberate choice. Sites that get those right feel considered, and they are usually running a record behind them.
The search side, briefly
Search work on a multilingual site is mostly the tags being right and the versions being genuinely different from each other rather than machine-copied. There is no separate trick: a correct hreflang set and a real translation is the whole of it, and everything else is the same work as a monolingual site done once per locale.
A site at four locales, counted
Take a hundred and twenty pages in English, German, Spanish and French. That is four hundred and eighty page-locale pairs if every page exists everywhere, and it never does: perhaps ninety pages in German, seventy in Spanish, forty in French. The hreflang set on each existing version names every other existing version and itself, so the German pricing page carries four links, the French help article that exists only in English and French carries two. The record that knows which pairs exist is the same record that generates the tags, feeds the switcher and answers which French pages are behind the English source. The free hreflang map on this site works the counts from your own page and locale figures, and the answer is usually the first time anyone at the company has seen the size of what they are maintaining.
What a bilingual website keeps that a four-language one cannot
A bilingual site keeps its second language current by habit: the person who wrote the English page writes the German one, or asks the one colleague who can. The knowledge of what exists lives in two heads. At four languages the third and fourth are translated by people outside the company, on a schedule, from a brief, and the source page changes after they finish. Without a row per page per locale with a status and a date, the site's own team cannot say which French pages describe the product as it was two releases ago, and the French readers find out for them. The record is not bureaucracy; it is the replacement for the two heads, and it is the part of a multilingual website that a bilingual one never needed.
Questions people ask about multilingual website
How many languages is too many?
As many as you can keep current. Four maintained locales beat eight where five are two years out of date, and stale translations are worse than none because they are still being read.
Should the site auto-redirect by country?
Suggest, never force, and always leave a way back. Forced redirects break crawling and infuriate the bilingual readers you most want.
Do we need separate analytics per locale?
Not separate properties, but you want the locale in the URL so you can segment. That is one more argument for subdirectories.
Should each locale have its own home page?
Yes, with its own canonical and its place in the hreflang set, and a language selector or x-default page for readers who match none. A single global home page that redirects by IP is the commonest way a multilingual site's crawling goes wrong, because the crawler and the reader are sent to different places.