Similar to the previous update which added a "variants" toggle to the anagrams mini game, adds variant toggles to the pairs, codeword and decipher mini games, along with the main board game. When off it will exclude words such as those from localised dialects (actually excludes words from the dictionary where there is an origin as well as those marked as obsolete).
Note that this option may be expanded upon in the future or removed. It might be expanded upon to allow selection of which dialects and origins to include or exclude. It might get removed as it could be replaced by the introduction of different dictionaries, although at the moment adding additional dictionaries would require keeping multiple lists up to date - hence added this option instead to reduce maintenance overhead.