In my understanding, each project would be written using only one programming language; however, today I learned that it is possible to combine different languages in one project.
For example:
Let's say we have a script written in Ruby*:

# my_ruby_script.rb
puts "Hello from Ruby!"

We can execute this Ruby script in a Python script*:

import subprocess

# Execute the Ruby script from Python
result = subprocess.run(['ruby', 'my_ruby_script.rb'], capture_output=True, text=True)

# Print the output of the Ruby script
print(result.stdout)

Although programming languages can be used together, mixing languages can make it more difficult to read and modify code; it must be done cautiously.

*Code examples from ChatGpt