I've a few technical questions.
1) I understand the FKKs are better in the suburbs and the rural regions (i.e., not Frankfurt downtown). Is English sufficient outside the major cities, as my German is quite iffy.
2) I MAY be travelling with friends of different racial backgrounds. How receptive are the girls there to non-WASPs (Jewish, East Asian, South Asian, Middle Eastern, Latino, African, etc.).
In my experience, FKK's are generally very accepting places where you're not likely to judged for your ethnicity or body type. I've seen all sorts of men frequenting them: older guys, younger guys, fat guys, thin guys, hairy guys, buff guys. I've seen lots of Turkish and Asian men at the bigger clubs though the smaller clubs are likely to frequented by locals.
I think you might have picked up some misleading information as far as your first point is concerned. Frankfurt is ground zero for FKKs. Four of the biggest in the area are among the best in the country and are constantly mentioned in FKK discussions.
Palace (north-west central Frankfurt):
www.the-palace.de
Mainhatten (east central Frankfurt):
www.fkk-mainhattan.de
Oase (suburb of Friedrichsdrf, about 20 km north of Frankfurt):
www.fkk-oase.de
World (Giessen, 60k north of frankfurt):
www.fkk-world.de
A fifth, FKK Beach, is okay but small, a bit dull and probably not worth your time:
www.f35.de
All of the big four are reasonably big, lavish places with 30 or more girls working evenings. Mainhatten is relatively new, so I can't really comment on it specifically, but the other three sometimes get singled out for the predatory behavior of some of the women. A lot of the clientelle are foreign businessmen passing through Frankfurt who don't speak German, are used to paying more for sex, and are seen as easy pickings by the most aggressive of the women. The Palace gets accused of this from time to time and I think that's where the notion that downtown Frankfurt is to be avoided comes from.
But no FKK is immune from this and I haven't found the women at The Palace to be any more guilty of predatory behavior, on average, than any other FKK. The fact is it's a great place with tons of stunningly sexy, exotic women to choose from. The Palace allows the girls to initiate contact with the guys, which is not the case at all FKK's, so you will sometimes get hustled by the relatively few women who you'd call sharks. You just have to be shrewd, like in any FKK, take your time to get a read on the girl's personality and ask some questions about her service levels before you commit to the room. Don't go with the first woman to approach you and avoid the ones who are in a hurry to get you into the room.
The huge advantage of Mainhatten and The Palace over Oase and World is that they're fairly easy to get to. Both are accessible by public transit.
All the FKK's in Frankfurt are premium priced. 65 euros to 80 euros entrance fee. 50 euros for each half hour with a girl. Extra fees for Greek and CIM though BBBJ is standard at all of them. The girls come from all over the world: Germany, Eastern Europe, Brazil, Thailand, China, the Caribbean, Africa. German is the language most widely spoken but you can get by with English at the bigger clubs and you can find lots of girls who speak English perfectly.
The FKK's get slightly cheaper, smaller and less internationally flavored as you move northwest or southwest of Frankfurt. The FKK's are very densely packed in the northern Rhine area between Cologne, Dusseldorf and the Dutch border and the entrance fees generally drop to between 30 euros and 50 euros, though the 50 euro for a half hour's service with the ladies is pretty standard. There are some overseas beauties but the bulk of the women are eastern Europeans who are less likely to speak English as a second language. As in Frankfurt, some of these FKK's are great and some aren't.
Some recommendations:
Samya (south central cologne):
www. samya.de. Mid-sized club with a good selection of international beauties and a fair number of out-of-town guys of all ethnicities attending
FKK Dolce Vita (south central Dusseldorf):
www.dolce-vita.com
In my opinion, the absolute best FKK in Germany, and the most expensive, is Artemis in west-end Berlin:
www.fkk-artemis.de. It's a multi-storey complex with several bars, a big spa area and an incredible selection of women. Very cosmopolitan atmosphere. 80 euro entry fee and 60 euros for a half hour's service.
I've heard good things about these FKK's in the rural northwest but I haven't been to any of them since they're awkward to reach and there isn't a lot of reason to be touring in this area otherwise:
Planet Happy Garden:
www.planet-happygarden.com
Golden Time:
www.goldentime.de
Villa Vertigo:
www.villavertigo.de
There are also some decent FKK's in the southwest border region with France in Stuttgart and around Karlsruhe. You might struggle to get by with just English here.