browserpass-extension: Unable to fetch and parse login fields

Just installed Browserpass extension in brand new Firefox installation on Mac OS Mojave. Native client has been installed using homebrew from brew tap amar1729/formulae. When trying to enter a password into a form, I see the following message instead:

Error: Unable to fetch and parse login fields: Error: {"status":"error","code":24,"version":3000006,"params":{"action":"fetch","error":"Error: exit status 2, Stderr: Warning: Failed to set locale category LC_NUMERIC to en_DE.\nWarning: Failed to set locale category LC_TIME to en_DE.\nWarning: Failed to set locale category LC_COLLATE to en_DE.\nWarning: Failed to set locale category LC_MONETARY to en_DE.\nWarning: Failed to set locale category LC_MESSAGES to en_DE.\ngpg: decryption failed: No secret key\n","file":"www/mywebsite.de/myusername.gpg","message":"Unable to decrypt the password file","storeId":"default","storeName":"pass","storePath":"/Users/myuser/.password-store"}}

Browserpass host app version: 3.0.6 Extension Version 3.1.1

I saw a similar note when using pass and gopass from the command line (missing LC_… etc). Then I found to add export LC_ALL=en_US.UTF-8 to .bash_profile which made both pass and gopass work. Then I tried to add the line to /etc/profile, but this did not work. Any ideas what can help?