In very broad terms, you probably want to define a gesture as a direction, followed by a [possibly very-short] delay, followed by another direction (and the relative angles between the directions, etc., until the end.
For example, making a "t" with your wand (and don't forget that some people are lefties, so your definitions should not be hand-dependant!) is a vertical swoosh, short delay, reversal curving out, short delay, reversal headed horizontal, abrupt [near] stop.
As you read the gesture, you want to see how closely the pattern read matches the pattern description.
In general terms, you can first cull the definition dictionary by eliminating obvious mis-matches (ones that don't even begin correctly, or that are too long or too short by far), then "score" the gesture against the remaining definitions. Score the gesture by rating each portion as to how well it matched the definition (0-100%) and RMS-ing that (take the errors, squared, sum them, then take the square root of that sum.)
Using RMS accentuates large differences (resulting in a lower score), while tending to gloss over small differences (resulting in a better match.)
There's a ton of material on this stuff -- Google gesture recognition. Don't worry if it's for a stylus or other non-Wii thing, the principles adapt well.