On a remote store installed into Plesk Error: STRING NOT FOUND is shown instead of all interface text strings.
OBAS store localization files are corrupted or absent on the Plesk server.
Store localization files are stored in /var/www/vhosts/storedomain.tld/httpdocs/i18n/ folder, where storedomain.tld is a name of the store domain. Let us say that the English localization is broken. To fix it, please copy the /var/opt/hspc-store/i18n/EN/hspc-store-basic.xml file from the OBAS server to /var/www/vhosts/storedomain.tld/httpdocs/i18n/EN/ on the Plesk server and make sure its permissions and ownership match the ones of the parent directory.