The Collaborative International Dictionary of English v.0.48:

Localism \Lo"cal*ism\, n.
   1. The state or quality of being local; affection for a
      particular place.
      [1913 Webster]

   2. A method of speaking or acting peculiar to a certain
      district; a local idiom or phrase.
      [1913 Webster]

WordNet (r) 3.0 (2006):

localism
    n 1: a phrase or pronunciation that is peculiar to a particular
         locality
    2: a partiality for some particular place [syn: sectionalism,
       provincialism, localism]

Moby Thesaurus II by Grady Ward, 1.0:

63 Moby Thesaurus words for "localism":
   Acadian, Anglo-Indian, Brooklynese, Cajun, Canadian French,
   Cockney, French Canadian, Gullah, Midland, Midland dialect,
   New England dialect, Pennsylvania Dutch, Yankee, Yorkshire,
   autarky, barbarism, bimetallism, bundle of isoglosses,
   class dialect, colloquialism, corruption, dialect, dialect atlas,
   dialect dictionary, economic self-sufficiency, free enterprise,
   free trade, governmentalism, idiom, impropriety, isogloss,
   laissez-faire, laissez-faireism, line, linguistic atlas,
   linguistic community, linguistic island, local dialect,
   managed currency, noninterference, nonintervention, nullification,
   party line, party principle, patois, planned economy, policy,
   polity, position, price supports, protection, protectionism,
   provincialism, public policy, pump-priming, regional accent,
   regionalism, sectionalism, slang, speech community, subdialect,
   taboo word, vulgarism