Because they are not TEXT, but they are PNG image. IF you have a Photoshop, then you can easily translate that ON SALE icon into your native language through the PSD file.
First open this PSD file with Photoshop: /templates/YOUR_TEMPLATE/html/com_virtuemart/assets/images/Flexible/FlexibleBadge.psd
Translate the texts, and save the file as PNG to this path: /templates/YOUR_TEMPLATE/html/com_virtuemart/assets/images/Flexible/FlexibleBadge.png