I added a comment to this issue: https://github.com/agentejo/cockpit/issues/962#issuecomment-465910232 as it seems there is a much larger problem with content language switching when editing collection items.
Values don’t get changed for at least
- localized image fields
- localized markdown fields when there are more than one in a collection (works only for the first one)
Posted this here also in case someone has a quick solution/workaround for this?