@kongondoThanks for your reply.
You are right, I am including PHP in my content. The main reason for this is, that I hate the built-in multilanguage-support as it does not separate formatting from content (i.e. when I want to move a picture in the german version, I have to move the picture in the english version explicitly as well).
There are other reasons too (i.e. image sizing). Your suggestion seems to be a very good idea for these, thanks.
If there were a system to handle my main concern (inline translation) and a syntax highlighter for the backend editor* I could be pursuaded to drop my php-file-idea entierly ?
Thanks again for your consideration.
* I have found i.e. Prism but not yet tried it as my localization-needs are my main concern.