Libby also works with many other libraries around the world and a bunch of them allow signing up for an account online.
For example, Abu Dhabi Department of Culture and Tourism has a nice collection and they only require an Emirates ID which is not too hard to get for visitors. The same is true for other public libraries in the UK. It's probably a good idea to sign up for library memberships wherever you travel!
You don't need any ID or registration for the one in Berlin (voebb.de). Just pay 10€ (not sure if international credit cards are accepted) and you are good to go for a year. Even had a 3 months trial without anything recently. Has a limited English section though.
Yes you're right, getting the Emirates ID depends on the visa type. But, there are lots of expatriates and people visiting for work or school who can get it/already have it. You can also almost always sign up using a passport in person and sometimes online too.
For example, Abu Dhabi Department of Culture and Tourism has a nice collection and they only require an Emirates ID which is not too hard to get for visitors. The same is true for other public libraries in the UK. It's probably a good idea to sign up for library memberships wherever you travel!