After adding two or more rules error: "Select a language for your function app by specifying FUNCTIONS_WORKER_RUNTIME AppSetting."

[pswetz]

After adding a second rule in a function instance the azure functions portal throws
"The function runtime is unable to start. Microsoft.Azure.WebJobs.Script: Found functions with more than one language. Select a language for your function app by specifying FUNCTIONS_WORKER_RUNTIME AppSetting."

Fix is adding setting to the instance
FUNCTIONS_WORKER_RUNTIME : dotnet