The installation of my slave site stalls at the database form. I can input all data (I tried with different mysql users) but the next button cannot be pressed, i.e. nothing happens. If I try to send the form via enter in one of the form field, the installation starts at the beginning.

Any help is appreciated. Thanks!

When you create a fresh slave site using the Joomla Installation, you have to proceed as usual to configure the DB parameters with the additional table prefix.
If Joomla does not allow you to continue, this is because your DB parameters are not correct.
If you want to use a new DB, some hosting provider require that you create the db with their own tool before using it.
If you want to share the existing DB, enter the same parameters than the websites that already used it. Don't forget to change the table prefix.

Thanks for your fast answer!

Unfortunately your hints didn't solve the problem.

I tried the following scenarios:
1) Using the name of the master-database and prefix en_ (for english site - master is in german)
2) Manually copying the masterdatabase to a new database and using this in the installation process.

I also tried root and the user which I have assigned to both databases (master ans copied one).

Nothing works so far. Is there a way (and template) to create the configuration.php for my multisites/en manually?

Thanks for your help!

If you use the same DB than your master, you can have a look in the configuration.php files located in the root of your master website.
You will find all the parameters required to have a correct DB connection.
Server, user name, password, and DB.
Don't forget to provide another table prefix.

If you want to replicate your master websites, you can also create a JMS "Website template" that will use the "master_db" as site to replicate.
After, you create a slave site using this "website template" and don't forget to provide a new table prefix.
This will replicate the master website into a slave site.

Thank you! The 2nd one helped!
And thanks again for the fast help!