Make sure that translation files of the Core plugin are placed in /wp-content/languages/plugins/ folder.
Then go to Loco Translate > Plugins > Core plugin > edit translation and click on the Sync button. Find and translate strings.
After every update, you need to synchronize translation – https://xstore.helpscoutdocs.com/article/103-translation-files-update Sometimes new strings are added, and only after synchronization, you’ll be able to translate new strings or strings that were changed. Not always, but some strings can be missing after the sync and you need to find and translate them one more time, this is independent of us and relates to WP functionality.
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