I do agree that "Select Page" is more clear than "Select all." In fact, it appears that the English translation file is already using the "Select Page" wording. Is it possible that we simply need to make a change to the German file to clarify this? If so, I would welcome a pull request.
Here at Villanova, we addressed this problem by simply raising the page size for favorites, which can be adjusted here:
Obviously you can't raise this indefinitely without running into memory issues, but we're using 100 with no problems so far.
I agree that the best solution of all might be an "export entire list" feature of some sort, and aspects of this have been discussed previously (for example, on pull request https://github.com/vufind-org/vufind/pull/436
, which was never completed). The bottom line is that if you have no upper bound on what can be exported, you will eventually find an extreme case that will either take an unreasonably long time or use an unreasonable amount of memory. The best solution to the problem would likely be to introduce an asynchronous job queueing system so that a user could request an export, kick off an asynchronous job, and receive notification when the job is ready to be retrieved... but that's a major new piece of infrastructure to add to VuFind. I think it could be beneficial, but it's a question of cost/benefit analysis -- so far nobody has had a pressing enough need to build such a thing. I remain open to discussing it further, though!