Translatable strings not displayed in frontend

[kaz]

I have installed Multi-language, activated the (Multi-Language) fields, added an additional language, and of course an language switcher. All content works fine, all fields are translated.

But translatable strings do not work. Here's an example:
<?php echo __("Kontakt");?>
or
<?php echo "<h6>" . $this->_('Kontakt') . "</h6>";?>
Under Languages I find the PHP file with the entry "Kontakt", I translate the text "Contact". But the translation is not visible in the frontend. What did I forget?

[kaz]

I have found why it does not work.
It only works with the ProFields module Functional Fields.