Re-divide the interpreters so that the length is the top-level grouping.
Preferences properly saved for multiple interpreter bars
Concept of an interpreter info which knows whether the interpreter will be fixed length in advance.
Additional combo box to choose a specific length when the interpreter is auto-length.
Split out the method for determining if there is a length option.
Break out the method to set a combo box to the square style.
Spelling
If the interpreter is fixed-length, just use the selection position and get the length from the interpreter itself.