Translated languages may reorder text resulting in parameters requiring to be in a different order. If the translator does not know the index format, i.e. %1$s, the message parameters may be inserted in the incorrect order.
We should add this index to messages generated in the skeleton file that is generally sent to translators. This should fallback to the default message if an error occurs determining the index. There should also be a way to disable this in cases where this may not be wanted or is causing issues. A message such as Parameter %s has an invalid value %s should be printed to the properties file as Parameter %1$s has an invalid value %2$s.