All effects created in Motion for Final Cut Pro are a collection of files in a folder. The folder IS the template. The contents of the folder should contain at least 3 files and one folder. That would be a large.png, a small.png, the Media folder (which will contain any external media required for use by the template) and the Motion Project file (ending in .moef, .motn, .moti or .motr).
All templates need to be placed inside a Category folder. The name of the category folder is the source for the name of the category that FCPX uses to organize templates within their "type collection" (Effects, Generators, Titles and/or Transitions).
The placement of your template folder is therefore:
/Users/<yourUserfolder>/Movies/Motion Templates/Transitions/<categoryFolder>/<transitionTemplateFolder>
The folders requiring ".localized" are: "Motion Templates" and the type collection level folder (which you have already taken care of).
The two most common missteps installing templates are 1) omitting the category folder step and 2) taking the .motr (or other) Motion Project file out of the template folder and attempting to place it in a category folder by itself. The name of the template (folder) MUST match the name of the actual template file (Motion Project file extension not included).
The arrangement of files used by FCPX is just an old fashioned "flat file database" taken from the Finder path data from a "root" of the Motion Templates folder. Using the finder data makes the data "live" and does not require maintaining an "internal" database of the available templates. Every time FCPX moves "to the front", it simply re-reads the file structure from Motion Templates down and updates any new additions (although restarting FCPX is necessary strongly suggested if templates are removed.
HTH