Update: Node-RED 1.2.9 is now available.
One of the fixes in 1.2.8 attempted to validate the language parameter passed into the api to ensure only valid values were used. That code was overly restrictive and treated some valid language codes as invalid. My apologies to our Latin American/Caribbean users who speak es-419
Node-RED 1.2.8 is now available for your enjoyment.
Full release details in the changelog: Release 1.2.8: Maintenance Release · node-red/node-red · GitHub
I had hoped we'd get 1.3-beta released by the end of this week, but that is looking unlikely - there are a couple pieces that we're still working on that I would like to get in before we release the beta. So stay tuned - it won't be too much longer.