What Does "Invalid HTML lang value" Mean?
The URLs have an HTML language tag that is not valid.
Language tags help screen readers, search engines, and other visitors to your site understand which language the content on the page is. Specifically, this is the "lang" global attribute that should be attached to the top-level <html> tag at the top of the document.
Here's an example of a typical HTML language tag:
The rules surrounding HTML tags can be surprisingly complicated. Dragon Metrics only looks for clear and obvious issues where an HTML tag is not valid.
Therefore, it's possible that even if a page is not flagged for this issue, it may not be technically correct. However, in this case most search engines will likely still be able to interpret them correctly.
Why It's Important
If the HTML language tag is not valid, it may cause search engines to have issues parsing, classifying, or indexing your site. It can also cause accessibility issues to visitors to your site, especially those using screen readers.
How To Fix
Take a look at the value for the HTML language tag for each URL. Replace the invalid value with the appropriate tag. For the vast majority of pages on the web, this is simply the ISO-639 two-letter language code, or ISO-639 two-letter code with ISO-3166 two-letter country code. Simply visit a code lookup table, and find the code that matches your content.
For less-common languages or other variations, it's possible to choose a code that is much more specific, with much more complicated rules. However, you should always try to use the simplest tag that fits your needs. For example, instead of "en-GB-Cyrl-u-kn-true-x-unproof-t-jp-032-Zxxx-x-matsu", consider using "en" in its place, unless you really feel there is a specific reason to do so.
For more information, we recommend reading the W3C's detailed description of this tag and how to choose a valid one.