Yes, you can install SQL Server 2014 Books Online locally
I've seen people complain that SQL Server 2014 did not ship with documentation you could install locally. While true, it is just because the publication lagged; the local Books Online option is available now.
First, make sure you have the documentation components installed. (Note that these use the old, icky, Help Viewer 1.0/1.1 – if you'd like to see this changed, vote here.)
Go to Control Panel / Programs and Features, select SQL Server 2014, right-click and choose "Add" and then point it at your ISO or installation folder. On the Installation Type screen, choose "Add features to an existing instance", select any 2014 (RTM or better) instance, and select Next.
On the Feature Selection page, make sure Documentation Components is checked. If it is already checked, hit Cancel to exit out of setup. Otherwise, check the box and hit Next. Setup will skip the remaining steps and offer you an Install button. You know what to do next. Should take less than a minute on an SSD.
Once it's installed, open SQL Server 2014 > Documentation & Community > Manage Help Settings (I almost suggested the Start Menu – which I still have, but you may not):
Click "Install content from online" and sit back and wait:
Enumeration here takes almost as long as the installation (depending on your bandwidth, I suppose). Scroll down to SQL Server 2014 and add Books Online (and the other two, if you wish):
This should take some time too.
When it's done, don't click Finish; click Settings, and make sure you've chosen local help:
Now you can launch the help viewer from SQL Server 2014 > Documentation & Community > SQL Server Documentation:
Now, there is some important content missing; SQL Server Database Engine > Transact-SQL Reference / XQuery Reference both yield "topic not found" – you may want to monitor this connect item and also periodically click the "check for updates" link in the Manage Help Settings app. In the meantime, you'll have to hit those topic online for real (Transact-SQL | XQuery).