To translate dbaas-controller's messages, we need to follow the next steps.
Use shared golang.org/x/text/message.Printer object's Sprintf method for messages that should be translated.
Do not use Sprint as it will not be collected on the next step.
Run make gen to collect new messages from source code and merge them with existing translations in messages.gotext.json.
The output of the command above will contain messages starting with "en: Missing entry for XXX".
That's new messages that should be translated in that file. Fill translation fields.
Run make gen to regenerate catalog.go file.
Compile Go program as usual (make release) to use updated translations.
Package catalog contains proper and user visible text of messages.
The goal is to fix syntax, grammar and other mistakes and improve readability in messages.