Currently it's not possible to translate the apply and reset buttons on the block translation page.
Update schema file, change button labels from string to label. This allows the fields to appear on the block translation tab.
Fixed
1.0
Code
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
@proweb.ua unfortunately the entity translation picks up the schema changes only on module install or re-install, in effect you would not translate configuration via string translation using t() but (after reinstall) enable the translation for block configuration.