I have been noticing over some time, that the correct language, set in the RW8 settings, does not get added to some projects. Some published pages have this important Language set correctly and some don’t have any language declaration, even when the language is et inside RW.
The first thing you should see in an index page (for each page) is something like:
Google PageInsights will flag it as an error if the language is not set.
After a conversation with Stuart (Shakingthehabitual), he wisely suggested selecting a different language in the RW - Settings - General, then putting it back to the language you want, and then Save.
This does fix the problem if you find you don’t have a language set.