Go to /demo-project/about/subsection-articles/article, edit a text image component, set an image caption value in en and in de, save.
When changing language, the values are correctly displayed due to the fact that they are served bases on the content node (content.imageCaption and content.imageCaption_de). fine.

The issue there is that model like InternalTeaserModel return an STKAssetWrapper and if the ftl would use this wrapper to display the image caption, we always displayed the default value.
InternalTeaserModel#getImage()

Original description --------------------------------------------------------------------------

assign assetList = damfn.getAssetsFromFolderId(content.link)
list assetList as assetNode
assign asset = damfn.getAssetMap(assetNode)
${asset.caption}
/#list

The asset always returns the values in the default language.

info.magnolia.dam.asset.Asset
info.magnolia.dam.asset.model.AssetMap