The two main branches are the current jan Pije and the stuff right after jan Sonja took down her lessons. I believe this one http://rowa.giso.de/languages/toki-pona ... essons.php
is somewhere in the middle, closer to the original jan Sonja lessons. The one on rowa.giso.de is my favorite.
I haven't actually seen much divergence in the toki pona that people are producing regardless to what lesson set they used or their mother tongue. An exception is "li pi" which is a mistake-- it's an odd-man-out construction and AFAIK only appears in the jan Pije lessons. I gripe about it at length elsewhere, no need to repeat.
I still, slow, slowly working on translating the current jan Pije lessons into Icelandic. Useful, I know : - ) I guess the underserved language groups are Hindi and Chinese-- I get very few hits to my toki pona fan site from South East Asia, China or the Indian subcontinent. I know there are smart polyglots there, but they have no access to suitable tp materials.
If I ever put my linguist hat back on, I might resume trying to fill out a Payne, Describing Morphosyntax style reference grammar. So many great projects, so little time.