I liked Shaheen style a lot back in the day, he doesn't sound american to me, but his rhymes, delivery, flow were on point, I personally love a lot of SA hip-hop, and don't really stress what accent it's in, as long as it sounds good.
I wouldn't stress how you freak your speech so much, it really just gotta sound good in the end, so if someone doesn't have a good handle of the language, and would be better off rhyming in their native tongue, then run it, if you freak it what ever language you do, the bottom line is, it has to sound good.
Again I'm not sure how you guys relate to the music, surely different than me from the outside looking in, as far as street credibility and authenticity goes, I'm not from there, but we've had very similar dilemmas in most non english speaking countries in europe, where a lot of artists have opted to rhyme in their native tongue, and ditched the english to gain more respect as far as credibility goes. Dutch MC's who I personally think are nice in English, like Brainpower, Cee Major, Rescue, Shockwave, catch flack for not rhyming in Dutch, I don't really trip, I think they are nice, a lot of those accusations stem from the peoples own insecurities, and what their idea of their fellow landsmen should sound like.
Again, we don't really have countries that speak 12 different languages, so that adds a whole new dynamic, my thing is as long as it sounds good, I wouldn;t really trip.
That doesn't mean it's gotta sound American either, most Dutch MC's who rhyme in Dutch, you can clearly tell where they are from. I liked Shaheen for instance a lot in the 90's, and he didn't sound American, but his rhymes were tight, his delivery was on point, and seeing P.O.C. live was one of my most memorable hip-hop moments to me.
Just My Two Cents....
peace