Who can help me to solve this problem? Abantecart?

Hello. As posted above you need to remove Non-existent brands from the Brands Scrolling List block
or modify public_html/storefront/controller/blocks/listing_block.php file
after line 319 add
// Skip if data source is vanished but still set in the listing.
 $result = array_filter($result);
see file https://github.com/abantecart/abantecart-src/blob/f45bee4742a9b6db2caf3975340ebf28f6a9c83d/public_html/storefront/controller/blocks/listing_block.php#L320

Hello.

You need to configure correctly your payment and gift certificate extension settings.
Please see attached screenshot.
Put your Payment method Order Status different from similar settings in Gift certificate extension. this will prevent sending the gift email until you change status of order.

Hello.

Please post site URL

It just needs to be easier for nondesigners/programmers to edit the color, font and layout of their site. People who don't want to bother will still want to buy templates.

http://marketplace.abantecart.com/fund-a-feature/new-free-improved-responsive-template-with-customization-tools

Hello ....
when i put an image url into' image resource or resource html section' the picture does not appear in store ,but just the url address as a hyperlink.
What have I done wrong?

Hello.

You need to upload image or add html code
http://forum.abantecart.com/index.php/topic,656.msg2166.html#msg2166

Please do not duplicate posts. http://forum.abantecart.com/index.php/topic,2817.msg12039.html#msg12039

Hello.

If you share your translation with us we can create an official language extensions based on the translation. 
Or you can create extension yourself and share it at AbanteCart marketplace http://marketplace.abantecart.com/developer

Hello.

Did you try Global Search in Admin? Or search in Admin-System-Localization-Language Definitions