Hi MaeseJesus,
I am not a RetroArch expert by any means, but I have been conducting some quick testing this week concerning 1.5 version (mostly snes9x2010, snes9x and fceumm cores) and it is good for turbo but it is unstable as hell. Snes9x2010 (snes9x next) have broken save states support (it ends up in dsi exceptions), switching from a rom loaded with fceumm to other core results in the same thing... Summing it up, that is one to avoid. Besides, if you read the changelog, no big optimization or fix has targeted the Wii in 1.5.
Next week I will be testing 1.2.2 and 1.4.1 versions. If you want me to perform some specific test, let me know.
Anyway, 1.0.0.2 is supposed to have some basic turbo functionality. I think that you need to designate a button as turbo "enabler" in the configuration and , once in the game, hold it down at the SAME TIME that the desired button that you want to have turbo. BUT, If you release the designated button = no turbo (you need to keep it pressed, like it was a combo). Sorry for my poor English language. That is what I have read in the libretro forums, not tested myself (yet!).
Regards!