We've got the same issue. We have Asset Serialization set to Force Text (it's a requirement of Unity Teams, but it's also just needed to make Unity be ok in source control), and as a result, I2 Localization is dropping the error:
"Binary to YAML conversion: type SInt64 is unsupported"
when we import the plugin from the asset store. I have no idea if it's still safe to use anyways, but I seriously doubt it?
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Asset Seraliziation setting to: force text
8 months 3 weeks ago #2722
If you don't import Examples, this error won't appear. Which means the error relates to an asset in the examples, not anything in the main library.
So you can just click the checkbox besides the Examples folder to not import them with the rest, that will remove the error, and presumably the main library is then perfectly safe to integrate into your source control / project / etc. I'm uncertain what specific asset in Examples isn't importing correctly, though. Hopefully it isn't the localization db or something - I'm going to dig a bit deeper.
EDIT: It's the scene files in Examples/Scenes. Disable that folder, everything imports fine. I'm going to guess the dev had Unity set up in a way that generated scenes which now can't be converted to text assets.