The source node in most cases contains the sample message as written by the developer. If it looks like a dot-delimitted string such as "form.label.firstname", then the developer has not provided a default message.

All customers All customers key: All customers Availability Availability key: Availability Currency code Currency code key: CurrencyCode Customer price group Customer price group key: CustomerPriceGroup Group A Group A key: Group A Group B Group B key: Group B Import was canceled: invalid currency %currency% in line %line% for sku: %sku% Import was canceled: invalid currency %currency% in line %line% for sku: %sku% key: Import was canceled: invalid currency %currency% in line %line% for sku: %sku% Import was canceled: invalid customerGroup %group% in line %line% for sku: %sku% Import was canceled: invalid customerGroup %group% in line %line% for sku: %sku% key: Import was canceled: invalid customerGroup %group% in line %line% for sku: %sku% Product not found Product not found key: message.product_not_found SKU not set SKU not set key: message.sku_not_set Duplicate entry found in line %line% of CSV file Duplicate entry found in line %line% of CSV file key: msg.error_duplicate_entry Column basic_price must be greater than 0! (line=%line% SKU=%sku%) Column basic_price must be greater than 0! (line=%line% SKU=%sku%) key: msg.error_upload_price_gt_zero_%line%_%sku% SKU must not be empty! (line=%line%) SKU must not be empty! (line=%line%) key: msg.error_upload_sku_empty_%line% Column stock must not be negative! (line=%line% SKU=%sku%)% Column stock must not be negative! (line=%line% SKU=%sku%)% key: msg.error_upload_stock_not_negative_%line%_%sku% No price was found No price was found key: msg.no_price_found Delivery costs %method% to %country% Delivery costs %method% to %country% key: msg.shipping_cost_name