Ahem, you can work with a placeholder in the language files and an if to ask for a setted timezone (forum or user) and an else for an empty string.

As I told you: it's just a little problem.

Did I miss something (codewise)?

The time difference which can still be set. If you set it, the displayed time doesn't correspond with the time zone. But that's just another little problem.

One question: It seems that the language files uses the INI-format. Is that true?

Similar. Smarty config files (German) are used for this purpose.