History demonstrates that diversity weakens.
Cultural groups mingled together are like chemical elements that won’t bond. In times of crisis or evident need of survival, cultural groups will seek their own and compete against others.
The Japanese don't give it away easily. They talk to neighbors, employers, coworkers and anyone else to ensure you will be an asset to the nation and not a liability. They also require that you demonstrate a reasonable proficiency with the language. Not native fluency, but functional fluency.
Some people call it racist, but when is the last time you heard about any jihadi incident in Japan?
The satanic lie that keeps being repeated about “diversity” and “strength” has been used to subvert and subject cultures since the beginning of time.