In the new image dialog xwiki-image, uploading images on non-English pages does not work as desired (you need to upload an image via the dialog to reproduce this). If you do this, the image is uploaded but linked incorrectly. In source code or wiki mode, there is an additional `attach:` in the path in all language versions, which is rendered as `attach%3A` in the image src path in HTML on non-English pages. The image is displayed during the editing process but not displayed in view mode after saving the page (broken link to source).
On English pages this does not happen, the image is displayed properly both in edit and view mode.