Java and PHP good union?

Question

PHP

Let's say there is an android application written in Java and backend in PHP. Will this be a good union, or is it better to write everything entirely in java (spring)?

Answer 1

The backend should have an API that can be pulled with requests from any language and from any system.
If it is, there will be a "good union" with any client.
If not, delete and rewrite.

Answer 2

What you know better - write on that.

Answer 3

From the point of view of supporting the project and reducing the cost of development, one language in the project is in theory better, but if this is not important, then write in whatever you know how, there will be no difference.