I have no experience with WP before. I tried to install WP 4.7 and have same problem. Only English was in dropdown list.
I thought WP downloads all translate files automaticall but unfortunately it didn't.
To get languages in dropdown list (Settings > General Settings > Site Language)
you need install translate files to
To download language file select version of WP here
than select language.
You will get a page where you can download language file.
For example for wp4.7 Ukraine I have got this page
At the end of the page find
Select 'all current' as 'Machine Object Messages Catalog (.mo)'
Then put downloaded file in wp-content/languages directory.
Open or refresh Settings > General Settings page.
You should see new language in dropdown list.
It is important to download .mo file exactly. I spent a lot of time trying to install .po file.
Also if you linux user and have only .po file you can convert it by command
msgfmt -o uk_UA.mo uk_UA.po
To install translate files for plugins and themes you should to do same things with some difference.
More details you can find here