CME has the FX options on their FX futures as well. ie at TD Ameritrade TOS platform.
Short strangles. If your a US resident- check out nadex binaries. They are also derivative of FX Spot. Open from 6pm to 5 pm on weeklies. Also there are daily and hourly expirations on fx.
The thing to consider is FX moving around the clock probably best to avoid a short strangle strategy where you can't adjust it during the evening (non NYSE hours) like on a FX ETF options. But with futures options should not be an issue also with nadex forex binary/spread options not an issue.
On the flip side - Long strangle/straddle - I prefer the their Spreads over the binaries usually but they are only hourly and daily no weekly but they are priced spot on with ie cme options. And are also available night and day.
If not in the US there are other choices also not sure of your location or how far out you are looking to do the strangle how much you want to adjust etc..are you gamma scalping etc.. etc..
Though this may really not be as technical as you where looking for. Liquidity... on Nadex look at the bid/ask size and the amount you are going to do that size stays pretty much the same so if that works for you then cool. On say cme or etf options - check out the open interest and volume and ensure you stay with say x percent 15% of open interest usually and 1/2 of the volume for easy entry/exit as a very "general" guideline.
Also compare all three side by side ETF, CME, Nadex etc.. see which risk/reward model etc.. works best for you account size strategy schedule etc...
Just a few ideas probably not the perfect answer but i hope it helps some.
If I wanted to sell OTM strangles on currency, what vehicle would you recommend (in terms of skew and liquidity )?