A webmaster-tools utility complains that my page is missing meta language information.
What should I do if my page contains mixture of text in multiple languages (all Western European languages)?
Most “webmaster-tools” complaints are best ignored (or not read at all). To get help with specific messages, please identify the tool, the message, and your URL.
A mixture of languages is a problem in itself, and best avoided by putting different language versions into different pages. If you need a mix of languages, use the lang attribute to specify the language of each part.
There is very little useful that you can do with meta tags, regarding a mixture of languages.