Margarita from Universidad de Cantabria informed me of a bug, which prevented Open Access Helper from installing on a Spanish language computer.
The source of this was a bad translation string in the messages.json for Spanish (and Italian, as I found out). This update fixes those typos AND brings the extension up to Manifest Version 3.
Manifest Version 3 is a new requirement for Chrome extensions and I am very excited about it. Please report any problems that you might find along the way.