A reasonable rate at which to consider a new primary programming language for non-niche, non-throwaway production software is once every 15 years. Adventurous, risk-seeking teams can try for 10, but that's pushing it.

If you find yourself searching for a replacement language more frequently, you should stop, take a long look in the mirror and ask yourself:

1. Something has clearly gone wrong last time, since you're looking for a replacement so soon; are you confident of your language-picking ability?

2. Are you sure your goal is to do what's best for the software and its long-term maintenance, or is there some other consideration here?