Code not working due to collation?
Learn about AUTO_INCREMENT instead of using max(directorID)+1.

moviedirector is a many:many mapping table.  See http://mysql.rjweb.org/doc.php/index_cookbook_mysql#many_to_many_mapping_table for optimal schema for such.  (may get you some brownie points)

"procedure unter MariaDB, it doe not work" elaborate.

(I see 2 clues so far that Deutsch is your native language.  But your English is great.)

SELECT directorID FROM director -- What is director?  It is not declared.  Stored Routines are tricky.  There are parameters (you prefixed them with par_ -- good); there are database/table/column names; there are @variables; there are DECLAREd variables; there are aliases (you don't have any); there are loop names (none).  Using the same 'name' for two different uses can cause mysterious errors.

Collation differences either lead to explicit errors or slow performance due to inability to use indexes.  So I don't think it is a collation problem.

I'm not sure, but I think the entire procedure can be replaced by a single INSERT .. ON DUPLICATE KEY UPDATE .. statement.