The following language plugins are installed:

Default language (English) 2.2.1+build.2018.09.11.16.46.02.170f744e4
en-GB English 2.2.1+build.2018.09.11.16.46.02.170f744e4
ja-JP Japanese 2.2.1+build.2018.09.11.16.46.02.170f744e4
CB Paid Subscriptions - en-GB 4.3.0+build.2018.09.19
CB Paid Subscriptions - ja-JP 4.3.0+build.2018.09.19

Despite the insistent indication that an update is required everything seems to be working, but I maintain these websites for non-technical clients and it is confusing for them to keep seeing this, which results in my having to respond to repeated requests to explain/fix it.

Where is Install from Web pulling version information to determine whether updates are required or not? Can I manually modify that file to make Install from Web think that the plugin is installed so that the Updates messages go away?

Is there a proper way to uninstall the language plugins? When I select them in Community Builder: Plugin Management and click delete I am told that core plugins cannot be deleted.

Also, when I reinstall, do I even need the English plugin? Or does the Default language plugin handle that? And do I need CBSubs language plugins? Or is that now handled by the CB language plugins?

I figured out the problem.

The reason that the CB Language plugins en-GB and ja-JP were causing issues is because for some reason the iscore column in the comprofiler_plugin table was set to 1 for each of them. Which would explain why I was unable to delete them from the CB Plugin Management interface (kept getting error message that core plugins cannot be deleted) and it is why they were being marked with an incorrect version number, which I suppose is why the Install from Web mechanism kept telling me that they needed updating. So, I deleted the 2 rows for the CB language plugins from the comprofiler_plugin table, deleted the corresponding folders from the server, then reinstalled the CB language plugins. They are now showing the correct version number inside CB Plugin Management and Install from Web no longer insists that they need updating.

I can't imagine how the iscore column got set to 1 as I have never touched or looked at that table! Anyway, issue resolved. Hopefully this might help others on the forum who have been reporting similar problems.