Hi Victor,

As I know it was fixed in last update 1.2.1+. In orginal ENGLISH language file (en-GB\com_easystore.ini) find those lines at the bottom area

;  Checkout Error Messages
COM_EASYSTORE_CHECKOUT_ERROR_TOKEN_MISSING="Cart token is missing"
; Checkout Field Validation Error Messages
COM_EASYSTORE_CHECKOUT_ERROR_CUSTOMER_NAME="Empty name field in address is not allowed"
COM_EASYSTORE_CHECKOUT_ERROR_ADDRESS_LINE_1="Empty address line 1 field in address is not allowed"
COM_EASYSTORE_CHECKOUT_ERROR_COUNTRY="Empty country field in address is not allowed"
COM_EASYSTORE_CHECKOUT_ERROR_CITY="Empty city field in address is not allowed"
COM_EASYSTORE_CHECKOUT_ERROR_ZIP_CODE="Empty zip code field in address is not allowed"
COM_EASYSTORE_CHECKOUT_ERROR_CUSTOMER_NUMBER="Empty phone number field in address is not allowed"

COM_EASYSTORE_CHECKOUT_ERROR_MESSAGE_COMPANY_NAME="Company Name is required"
COM_EASYSTORE_CHECKOUT_ERROR_MESSAGE_VAT_INFORMATION="VAT information is required"

COM_EASYSTORE_CHECKOUT_ERROR_MESSAGE_EMAIL="Email is required"
COM_EASYSTORE_CHECKOUT_ERROR_MESSAGE_PAYMENT_METHOD="Payment Method is required"


COM_EASYSTORE_CHECKOUT_ERROR_MESSAGE_SHIPPING_METHOD="Shipping Method is required"

COM_EASYSTORE_CHECKOUT_ERROR_MESSAGE_CUSTOMER_NAME="%1$s customer name is required"
COM_EASYSTORE_CHECKOUT_ERROR_MESSAGE_COUNTRY="%1$s country is required"
COM_EASYSTORE_CHECKOUT_ERROR_MESSAGE_STATE="%1$s state is required"
COM_EASYSTORE_CHECKOUT_ERROR_MESSAGE_CITY="%1$s city is required"
COM_EASYSTORE_CHECKOUT_ERROR_MESSAGE_ZIP_CODE="%1$s zip Code is required"
COM_EASYSTORE_CHECKOUT_ERROR_MESSAGE_ADDRESS_LINE_1="%1$s address Line 1 is required"
COM_EASYSTORE_CHECKOUT_ERROR_MESSAGE_ADDRESS_LINE_2="%1$s address Line 2 is required"
COM_EASYSTORE_CHECKOUT_ERROR_MESSAGE_PHONE_NUMBER="%1$s phone is required"

; Field Error Message
COM_EASYSTORE_ERROR_MESSAGE_REQUIRED_FIELD="Field is required" 
COM_EASYSTORE_ERROR_MESSAGE_PATTERN_FIELD="Value does not match the pattern" 
COM_EASYSTORE_ERROR_MESSAGE_EMAIL_FIELD="Invalid email address" 
COM_EASYSTORE_ERROR_MESSAGE_INVALID_JSON_FIELD="Invalid JSON format for nested"
; Invoice
COM_EASYSTORE_ORDER_INVOICE_PRINT="Print"

Then copy-paste to your native language file (.ini), and translate

ua-UA\com_easystore.ini ??