utf8 characters wrongly displayed as question marks after conversion to mysqli_query()

My database is latin1_swedish_ci but all the tables which contain foreign characters (german, turkish...) are utf8_general_ci.

Before the upgrade to php 5.6, I used mysql_query("SET CHARACTER SET utf8;");mysql_query("SET NAMES utf8"); before mysql_query() and everything was displayed correctly in my page ( in page header).

After the conversion of all mysql_query(...) to mysqli_query(id,...) and running under php 5.6, all the foreign languages are now scrambled with ? and �. Switching back to php 5.4 does not help. phpMyAdmin displays the mysql database (which has not changed) correctly.

I have looked around for a solution but nothing works... am I missing something?

What do I need to change in my code to work properly?