As mentioned above I second apple maps for navigation- it has been the best option for us over the last 8 months in Beijing. Very accurate, with transit options shown.

I saw DiDi mentioned in passing above, I would recommend downloading that (English version is slightly more limited than the Chinese one, but really has everything you should need, and has pre-set pick up points and auto translates messages to/from the driver). Bonus is you can use a foreign credit card (and phone number) while in China.

WeChat does have a translate function that is pretty accurate most of the time (under their scan function) which is useful when translating signs and the like. I would also recommend downloading the Chinese database for google, it can come in handy and they claim they just improved their camera function (haven't tested it yet).