That could be a nice middle ground. It seems that neither pontoon nor weblate can directly handle MD files. Weblate has support for simple text files in beta, however. A README file is given as an example, which is often in MD, so it might work.
From an SO question it seems that new items can be created in Weblate automatically if new (site) content is added. But it seems that it’s still best to transform MD files to PO files first. Would be great if that could be automised in a GitHub action, but couldn’t find any hints or marketplace item for this.