Apparently new XWiki Page properties files created by weblate are missing the language tag, see: https://github.com/xwiki-contrib/application-paragraph-numbering/commit/6e8aba1bc9aea271c1da14f7e5ce8064612bf6a6#diff-04f094176a83714e3654d8abac05a7f68d781ceb2e502ee35826de655591fb44R26
This seems to be a recent regression.