User Agent: Mozilla/5.0 (X11; Linux i686) AppleWebKit/537.36 (KHTML, like Gecko) Ubuntu Chromium/64.0.3282.140 Chrome/64.0.3282.140 Safari/537.36 Steps to reproduce: Using ubuntu 14.04 32-bit (german version), I installed from scratch: Thunderbird 52.6.0 32-bit Lightning 5.4 Add one event to the calendar Export into .csv file Delete the previously added event from the calendar Try to import the .csv file Actual results: Konnte nicht von Datei lesen:/home/rseitzde/tmp/MeinKalender.csv [Exception... "[JavaScript Error: "locale is not defined" {file: "resource://calendar/modules/calUtils.jsm -> file:///home/rseitzde/.thunderbird/3cae9v06.default/extensions/%7Be2fda1a4-762b-4020-b5ad-a41df1933103%7D/calendar-js/calOutlookCSVImportExport.js" line: 245}]'[JavaScript Error: "locale is not defined" {file: "resource://calendar/modules/calUtils.jsm -> file:///home/rseitzde/.thunderbird/3cae9v06.default/extensions/%7Be2fda1a4-762b-4020-b5ad-a41df1933103%7D/calendar-js/calOutlookCSVImportExport.js" line: 245}]' when calling method: [calIImporter::importFromStream]" nsresult: "0x80570021 (NS_ERROR_XPC_JAVASCRIPT_ERROR_WITH_DETAILS)" location: "JS frame :: chrome://calendar/content/import-export.js :: loadEventsFromFile :: line 85" data: yes] Hint: Open terminal and enter "locale" returns: LANG=de_DE.UTF-8 LANGUAGE=de_DE:en LC_CTYPE="de_DE.UTF-8" LC_NUMERIC=de_DE.UTF-8 LC_TIME=de_DE.UTF-8 LC_COLLATE="de_DE.UTF-8" LC_MONETARY=de_DE.UTF-8 LC_MESSAGES="de_DE.UTF-8" LC_PAPER=de_DE.UTF-8 LC_NAME=de_DE.UTF-8 LC_ADDRESS=de_DE.UTF-8 LC_TELEPHONE=de_DE.UTF-8 LC_MEASUREMENT=de_DE.UTF-8 LC_IDENTIFICATION=de_DE.UTF-8 LC_ALL=

Not so nice workaround, but it helps: As .ics export/import is working, just convert .csv file into .ics by using e.g. Google Calendar import/export.

This has already been fixed for Lightning 5.4.3 - please update your Lightning version.