So what works?

Coding guidelines? - These are safe if they deal with "accents", but can entrench obscure and obsolete dialects unless they are carefully reviewed, living documents that change as ideas are revised. See http://groups.yahoo.com/group/boost/files/coding_guidelines.html for a good example.
Training courses? - These can expose those that attend to new idioms, but they cannot ensure ideas are either internalised or adopted by others.
Code Reviews? - If properly conducted these can help the team settle on a common dialect, or at least become familiar with those in use. On the other hand they can be a cause of friction and entrenchment.
Pair programming? - If properly conducted these can help the team settle on a common dialect, or at least become familiar with those in use. On the other hand they can be a cause of friction and entrenchment.
Coaching/mentoring? - Good coaches/mentors are hard to find. Bad ones are worse than useless.

Coding guidelines? - These are safe if they deal with "accents", but can entrench obscure and obsolete dialects unless they are carefully reviewed, living documents that change as ideas are revised. See http://groups.yahoo.com/group/boost/files/coding_guidelines.html for a good example.