Set the document language in every PDF
Every PDF should declare its default language in the Lang entry of the document catalog. W3C gives three reasons, and only the first is the obvious one. Screen readers load the correct pronunciation rules, visual browsers display characters and scripts correctly, and media players show captions correctly. W3C publishes PDF16 as a sufficient technique, and it is one of only three techniques W3C documents for declaring a page's language at all, two of which are PDF techniques. In Acrobat Pro it is one dropdown, under File, Properties, Advanced, Reading Options, and tagged exports from Word and InDesign normally set it for you. Few fixes are cheaper.
How we find it in an audit
We check Document Properties in Acrobat for the language setting and listen to the opening paragraphs with a screen reader. Wrong-language pronunciation is unmistakable within a sentence. Where we need to be certain rather than confident, we read the Lang value in the document catalog directly. Acrobat's accessibility checker also flags a missing entry.
How affected users experience it
A German contract read with an English synthesizer is pronounced by English rules, and real words become sludge. It is the difference between a document in your language and a document in no language at all, and many users simply close it and ask for help they should not need.
Passes vs. fails
Passes
The document catalog carries Lang fr-FR. Screen readers switch to a French voice automatically and the policy reads as French.
Fails
A French insurance policy has no Lang entry. An English-voiced screen reader mangles every sentence of "les conditions générales" into noise.
How this gets tested
The W3C publishes test rules that define what a checker looks for here.
- HTML page has lang attributeA tool can check this
- HTML page lang attribute has valid language tagA tool can check this
- HTML page language subtag matches default languageA tool can check this
Other ways to satisfy this rule
4 guides on this site are filed under 3.1.1 Language of Page. W3C lists this one as sufficient for that rule on its own. Implement it correctly, in a way your readers' software actually supports, and the rule is met.
This guide is our interpretation of W3C technique PDF16: Setting the default language using the /Lang entry in the document catalog of a PDF document. W3C publishes its techniques as guidance rather than as the standard, and says so on every one of them. The success criterion is what conformance is measured against, and a technique is one documented way to meet it.