Translating your site is the growth tactic everybody considers and almost nobody finishes. You get three languages in, the translations drift out of date, and two years later you are quietly deleting them.
MDN is the reference every web developer has open in a tab. We counted it expecting a large English documentation set.
English turned out to be about a fifth of it.
Results at a glance
MDN writes about 14,600 English documentation pages and publishes 66,772 URLs.
The difference is the same material, in nine other languages.
One corpus, ten languages
MDN makes this unusually easy to measure, because it publishes one sitemap per language rather than mixing them together.
The English corpus is 14,738 URLs, and 14,601 of those are under /docs/. Everything else — the blog, the curriculum, the community pages — comes to about 130 pages in total.
So MDN maintains one thing: a reference manual of roughly fourteen and a half thousand pages. Then it publishes that manual four and a half times over.
The same page, twice
The obvious worry with any translated corpus is that the translations are thin — a title, a stub, a note saying this page has not been translated yet.
We checked the overlap properly rather than eyeballing it. Of the 7,624 French pages, 100% correspond to a real English page. Chinese: also 100%. Japanese: 99.7%. Spanish: 96%.
So there are essentially no orphans — no translated pages floating without a source, which is the usual sign of a localisation effort that has lost track of itself.
Where the translators actually are
The gradient between languages is the most useful thing in this case study, because it is a map of where sustained volunteer effort exists.
German is at 99.2% of English. Japanese 69.4%. French and Simplified Chinese both around 51%. Then it drops: Korean 22.9%, Russian 19.1%, Spanish 18.3%, Brazilian Portuguese 13.8%, and Traditional Chinese at 7%.
That gradient has consequences you can check. /en-US/docs/Web/CSS/flex and /de/docs/Web/CSS/flex both load. /zh-TW/docs/Web/CSS/flex returns a 404 — one of the most-used properties in CSS has no Traditional Chinese page at all.
Notice also what is not here. Ten languages, for the reference manual of the entire web platform. No Hindi, no Arabic, no Italian, no Polish. A site of this importance could plausibly list forty locales and have thirty of them half-finished.
What a translated corpus earned
260,658 referring domains across 66,772 pages is 3.9 referring domains for every page — behind only calculator.net and Healthline in this series, and far ahead of every other site of comparable size.
89% of those links are dofollow. Developers link to MDN from documentation, from Stack Overflow answers, from code comments and from their own blogs, and those are real editorial links rather than citations in an argument.
The honest reading is that the translations are not what earned this. The English reference did. But the translated pages inherit a domain that has been linked to for twenty years, which is precisely why translating is such an efficient move for a site that already has authority — and such a poor first move for one that does not.
Copy this in an afternoon
Translation is the cheapest page multiplier that exists, and the easiest one to do badly.
1. Translate the reference, not the blog. MDN's blog is 72 pages and stays in English. The 14,601 documentation pages are what got translated, because reference material stays true and news does not.
2. Publish one sitemap per language. It is how MDN made this measurable, and it is how you will notice when a locale stops being maintained.
3. Do not open a locale you cannot sustain. Ten languages, four of them under a quarter complete, is already a visible gradient. Forty would be a graveyard.
4. Check your orphans. Take every translated URL, strip the locale prefix, and confirm the English page exists. MDN scores 96 to 100% on that test. A failing score means you are publishing pages nobody can trace back to a source.
What you cannot copy
People who translate for free because they need the page to exist. MDN's German coverage is not a budget line, it is a community that wants the reference in its own language. If you have to pay for every page, translation stops being a cheap multiplier and becomes the most expensive content you own — and it needs re-paying every time the source changes.
And here is what we could not check:
We did not assess translation quality. We measured coverage and structure — whether pages exist and whether they map to a real source. Whether the German prose is any good is not something our tools can tell you.
Nor how current they are. A translated page that exists may still be describing an older version of the source. Coverage and freshness are different problems and we only measured one.
Declared pages are not indexed pages. 66,772 is what the sitemaps list on one day.
No traffic data. None was available and none is claimed.
Translation multiplies whatever authority you already have. If you have very little, it multiplies very little. The Backlink Analyzer returns your referring domain count in about a minute, so you can find out which situation you are in before you commission a word.
- The same check that returned domain rank 100 for MDN
- Referring domains, anchors and the follow split, counted separately
- 3 checks a day, no signup, no card
Frequently asked questions
How big is MDN?
66,772 URLs across 10 language sitemaps, counted on 29 August 2026 by fetching every file rather than sampling, with no errors. English accounts for 14,738 of them, or 22.1%.
How complete is each language?
As a share of the English corpus: German 99.2% (14,627 pages), Japanese 69.4% (10,233), French 51.7% (7,624), Simplified Chinese 51.5% (7,591), Korean 22.9% (3,370), Russian 19.1% (2,813), Spanish 18.3% (2,697), Brazilian Portuguese 13.8% (2,041) and Traditional Chinese 7.0% (1,038).
Are the translated pages real pages or stubs?
Real pages. We compared the German and English versions of the same CSS reference page: identical structure, the same interactive example and specification tables, with all prose, headings and the page title translated. We also checked for orphans by stripping the locale prefix from every translated URL — 100% of French and Chinese pages, 99.7% of Japanese and 96% of Spanish correspond to a real English page.
What does the coverage gap look like in practice?
/en-US/docs/Web/CSS/flex and /de/docs/Web/CSS/flex both return 200. /zh-TW/docs/Web/CSS/flex returns 404. One of the most commonly used properties in CSS has no Traditional Chinese page, which is what a 7% coverage figure means when you land on it.
What is in the English corpus besides documentation?
Very little. Of 14,738 English URLs, 14,601 sit under /docs/. The remainder is 72 blog posts, 27 curriculum pages, 14 community pages, 12 plus pages and a handful of others. MDN is a reference manual with a small amount of everything else attached.
What is its backlink profile?
Domain Rank 100 out of 100 — the first perfect score in this series — with 36,283,966 total backlinks from 260,658 referring domains, 33,900,922 dofollow and 4,021,179 nofollow links, 111,167 referring IPs and 56,617 referring subnets. That is 3.9 referring domains per page and an 89% dofollow share.
What did the website audit find?
88 out of 100, with 0 critical issues, 1 warning and 5 notices against 115 checks passed. On-page SEO 23 of 25, technical SEO 63 of 67, speed 28 of 29, mobile 2 of 2. The warning was outbound links pointing at dead pages; the notices covered redirects, missing link anchors and unminified JavaScript. The meta description is 145 characters and there is one clear H1.
Should I translate my site?
Only after you have something worth translating and the authority to carry it. Translation multiplies what you already have: a strong domain with a genuinely useful reference gets a large, cheap expansion, which is what happened here. A weak domain with thin content gets the same thin content in six languages and a maintenance burden that grows every time the source changes. Check your referring domain count first.
The number that stays with us is 14,601. That is how many documentation pages MDN actually writes, and it is a corpus a determined team could genuinely maintain.
Everything else on the domain — three quarters of it — is that same work, said again for somebody who needed it in their own language.
Run the check on your own domain and find out whether you have authority worth multiplying.
Measured on 29 August 2026. Page counts come from developer.mozilla.org's own sitemap files; all 10 language sitemaps were fetched and counted rather than sampled, with no errors, but declared URLs are not indexed pages. Coverage percentages are page counts against the English corpus, and say nothing about translation quality or freshness.
Link and audit figures are free runs of our own tools, and the comparisons use the same tool earlier in this series. No traffic data was available to us and none is claimed here.