This app was mentioned in 4 comments, with an average of 1.25 upvotes
Get a VPN before you travel to China! I used Baidu Map instead of Google Maps when I was in China, although it's only in Chinese but I found it pretty straight forward to use (with my location turned on).
Betternet
Metro signs and street names are in English/pinyin too. Some restaurants have English names on the menu. You can get by with English but probably with difficulties.
Don't know about Google Maps offline, but you can try Baidu Maps https://play.google.com/store/apps/details?id=com.baidu.BaiduMap and I use this Metro app that works offline: https://play.google.com/store/apps/details?id=com.exploremetro.sh
Have fun!
baidu's map app has an offline mode, but it's not exactly bilingual. Google probably does too, but I've never used it.
The big 3 for maps are Baidu, QQ and AutoNavi.
https://play.google.com/store/apps/details?id=com.baidu.BaiduMap&hl=en
https://play.google.com/store/apps/details?id=com.tencent.map
https://play.google.com/store/apps/details?id=com.autonavi.minimap
I personally find Chinese apps to vary wildly in quality. For example, once I went hiking and had baidu maps in the background, it burnt through all my battery in 2 hours.
You can also try Yahoo Maps and Bing Maps.