Depends on how experienced you are in general. if you're not experienced, you'll probably struggle quite a bit, if you're experienced, you'll pick up the new language quickly. Dart for example i used two years before it was considered production ready and by the time my project was nearing completion, it became production-ready. Kotlin i only started using when it hit 1.0.0
If you have a fixed deadline for your project, don't jump into a new language, use something that you're familiar with, unless you budget a lot of extra time into learning the new language as well.