Both tags are synonyms, but they are not marked as such. Both have 3 questions tagged with one of them. Can someone make them synonyms?
Thanks for the catch. We don't always know what the tag situation is and it's useful to have other users help the moderators to clean/fix the site, tags included.
Tag synonyms have now been created and merged. If someone uses sociolinguistics, it will be replaced by the Russian equivalent.