Convert MySQL database from latin1 to utf8mb4 - and take care of German umlauts
There are two possible questions here, and they have two different answers --

How do I make all new tables utf8mb4

It can be done (for one database) while creating a database:

CREATE DATABASE dbname
    DEFAULT CHARACTER SET utf8mb4
    DEFAULT COLLATE       utf8mb4_unicode_ci;


You can ALTER a database (similar syntax), but that only provides a default for future tables.

There are bugs relating to inheriting from the 'server' variables:  http://dev.mysql.com/worklog/task/?id=3811 , so I suggest that you simply be explicit on each database.

How do I convert existing latin1 tables

If you have a table declared to be latin1 and correctly contains latin1 bytes, and you would like to change all the char/text columns to utf8...

ALTER TABLE tbl CONVERT TO CHARACTER SET utf8mb4;


This changes the definition and actively changes the necessary bytes in the columns.

ALTER TABLE tbl MODIFY col1 ... CHARACTER SET utf8mb4;


is similar to the above, but works only one column at a time, and needs
exactly the right stuff in the MODIFY clause.  Hence, it would be quite tedious.  However, it is useful if you want to change only some of the columns.