Document language is missing or invalid

Messages you may see

• Acrobat Accessibility Checker: Primary language - Failed (Text language is specified)
• PDF/UA-1 (ISO 14289-1) rule 7.2-34: Natural language for text in page content shall be determined
• PDF/UA-1 (ISO 14289-1) rule 7.2-29: If the Lang entry is present in the document's Catalog dictionary or in a structure element dictionary or property list, its value shall be a language identifier as described in ISO 32000-1:2008, 14.9.2. A language identifier shall be a Language-Tag as defined in RFC 3066, Tags for the Identification of Languages
• PDF/UA-1 (ISO 14289-1) rule 7.2-33: Natural language for document metadata shall be determined
• PDF/UA-1 (ISO 14289-1) rule 7.2-22: Natural language for text in Alt attribute shall be determined
• PDF/UA-1 (ISO 14289-1) rule 7.2-2: Natural language in the Outline entries shall be determined
• PDF/UA-2 (ISO 14289-2) rule 8.4.4-1: The default natural language for content and text strings shall be specified using the Lang entry, with a non-empty value, in the catalog dictionary
• Matterhorn Protocol 1.1, 11-001: Natural language for text in page content cannot be determined.
• Matterhorn Protocol 1.1, 11-006: Natural language for document metadata cannot be determined.

What the rule requires

PDF/UA-1 (ISO 14289-1, clause 7.2) requires that the natural language of all text can be determined. The language can come from the /Lang entry in the document catalog, from /Lang on a structure element, or from a Lang property in marked content. Automated checkers test each kind of text separately:

• page content (rule 7.2-34), document metadata (7.2-33) and bookmarks (outline entries, 7.2-2)
• alternative text, replacement text and expansions in Alt, ActualText and E (7.2-21 to 7.2-23, and 7.2-30 to 7.2-32 for marked content)
• annotation contents (7.2-24) and form field tooltips in TU (7.2-25)
• the format of every /Lang value (7.2-29): it must be a language tag as defined in RFC 3066, for example de, de-DE, en-GB

In practice, a single valid /Lang in the catalog makes all of these determinable at once, because every text inherits the default language. That is why one missing entry often produces many findings. PDF/UA-2 (ISO 14289-2) makes the catalog entry explicit: rule 8.4.4-1 requires a non-empty /Lang in the catalog, rule 8.4.4-2 a valid language tag.

In the Matterhorn Protocol 1.1 this is checkpoint 11 (Declared natural language), failure conditions 11-001 to 11-006. Condition 11-007, “Natural language is not appropriate”, is a human check.

Why it matters

Screen readers choose their pronunciation rules, and often the synthetic voice, from the declared language. If a German document is declared as English, or declares nothing and the screen reader falls back to its own default, words are pronounced with the wrong rules. Long texts become very hard to follow, and names, numbers and abbreviations are read incorrectly.

Passages in another language need their own declaration. An English quotation in a German report, read with German pronunciation, may be incomprehensible. The same applies to alternative text and form field descriptions, which are read aloud just like body text. WCAG success criteria 3.1.1 (Language of Page) and 3.1.2 (Language of Parts) cover these two cases; the W3C techniques PDF16 and PDF19 show how to meet them in PDF.

Common causes

• The PDF was created by a tool that writes no /Lang at all, for example a PDF printer driver, a scanner or a simple PDF library.
• In Word, the language assigned to the text does not match the actual language, often because the template or keyboard setting assigned English (United States) to German text.
• In InDesign, no language was chosen in the export dialog; older InDesign versions had no such setting, and Adobe's older guide therefore recommends setting the language in Acrobat.
• The value is malformed: German, de_DE with an underscore, or an empty string. These are not valid language tags.
• Several PDFs in different languages were merged, and only the first one carried a language entry.

Example

1 0 obj
<< /Type /Catalog
   /Pages 2 0 R
   /StructTreeRoot 5 0 R
   /MarkInfo << /Marked true >>
>>
endobj

% invalid values:
/Lang (English)
/Lang (en_GB)

1 0 obj
<< /Type /Catalog
   /Pages 2 0 R
   /StructTreeRoot 5 0 R
   /MarkInfo << /Marked true >>
   /Lang (en-GB)
>>
endobj

% a German quotation inside an English paragraph
34 0 obj
<< /Type /StructElem /S /Span /P 33 0 R
   /Lang (de-DE)
   /Pg 8 0 R /K 5 >>
endobj

How to fix it

Microsoft Word

1. Select the whole text with Ctrl+A.
2. Choose Review > Language > Set Proofing Language, select the language of the document and confirm.
3. Select each passage in another language and assign its language in the same way.
4. Save as PDF with File > Save As > PDF > Options and Document structure tags for accessibility checked.

To avoid the problem in new documents, set the preferred authoring language under File > Options > Language. Microsoft also suggests automatic language detection (Review > Language > Set Proofing Language > Detect language automatically, which applies to the current document); if you use it, check short passages, because detection can assign the wrong language to names or single words.

Adobe InDesign

1. Choose File > Export, select Adobe PDF (Print) or Adobe PDF (Interactive), and open the Advanced tab.
2. Choose the document language under Language. If your language is not listed, Adobe's help says you can type a standard ISO language code.
3. Assign the correct language to passages in other languages in their character or paragraph style (Advanced Character Formats > Language). This setting also controls hyphenation and spell checking.
4. Export and check in Acrobat whether the passages carry their language; if not, set it there as described below.

Adobe Acrobat Pro

1. Run All tools > Prepare for accessibility > Check for accessibility. Open the options menu of Primary language, choose Fix, select the language in the Set Reading Language dialog box and select OK.
2. Manual route: hamburger menu (Windows) or File menu (macOS) > Properties > Advanced. Choose the language in the Reading Options section. If it is not in the list, enter the ISO 639 code in the Language field.
3. For a passage in another language, open the Accessibility tags panel, select the element, choose Properties from the options menu and pick the language.
4. Save and check again.

Questions

Should I use de or de-DE?

Both are valid. The region subtag is optional; it can help speech output with regional spelling or pronunciation, for example en-GB versus en-US.

The catalog has a language, but findings for alternative text or bookmarks remain. Why?

Usually the catalog value is invalid or empty, so nothing can be inherited. Less often, a structure element declares an invalid /Lang of its own. The findings in our report list the affected objects.

Sources

1. ISO 14289-1:2014 Document management applications – Electronic document file format enhancement for accessibility – Part 1: Use of ISO 32000-1 (PDF/UA-1) – International Organization for Standardization (ISO). Checked on 7 November 2026.
2. ISO 14289-2:2024 Document management applications – Electronic document file format enhancement for accessibility – Part 2: Use of ISO 32000-2 (PDF/UA-2) – International Organization for Standardization (ISO). Checked on 7 November 2026.
3. The Matterhorn Protocol 1.1 – PDF Association. Checked on 7 November 2026.
4. Matterhorn Protocol checks (list of checkpoints and failure conditions) – PDF Association (Tagged PDF School). Checked on 7 November 2026.
5. RFC 3066: Tags for the Identification of Languages – IETF (RFC Editor). Checked on 7 November 2026.
6. PDF16: Setting the default language using the /Lang entry in the document catalog of a PDF document – W3C Web Accessibility Initiative (WCAG 2.2 Techniques). Checked on 7 November 2026.
7. PDF19: Specifying the language for a passage or phrase with the Lang entry in PDF documents – W3C Web Accessibility Initiative (WCAG 2.2 Techniques). Checked on 7 November 2026.
8. Create and verify PDF accessibility, Acrobat Pro – Adobe (Acrobat User Guide), 23 July 2025. Checked on 7 November 2026.
9. Edit document structure with the Content and Tags panels (Adobe Acrobat Pro) – Adobe (Acrobat User Guide), 3 May 2025. Checked on 7 November 2026.
10. Change the language Office uses in its menus and proofing tools – Microsoft Support. Checked on 8 November 2026.
11. Create accessible PDFs – Microsoft Support. Checked on 8 November 2026.
12. Creating accessible PDFs – Adobe (InDesign User Guide), 24 May 2023. Checked on 7 November 2026.
13. Interactive PDF export options in InDesign – Adobe (InDesign User Guide), 2 June 2026. Checked on 7 November 2026.