In the latest update (version 7.0.24, on OSX), when merging duplicates, the GUI button shows "Merge {$count} items" instead of interpolating the value and showing, e.g., "Merge 3 items".
I don't know, I am not interfering with the dialog or with Zotero translations. I am monkey-patching Zotero.Items.merge but I don't see how that could cause this.
Doesn't mean to make the discussion too technical, but it might be the case that BBT is inserting FTL files while they are not properly removed when the plugin is shut down. See this as an example to remove the ftl files from the main window (which should also be called on plugin shutdown).
Upgrade Storage
FWIW the only plugin I have is Better Bibtex for Zotero.
Doesn't mean to make the discussion too technical, but it might be the case that BBT is inserting FTL files while they are not properly removed when the plugin is shut down. See this as an example to remove the ftl files from the main window (which should also be called on plugin shutdown).