The format "1; {$testString$}" works fine for me. Make sure you have no spaces or other whitespace characters in place. Check also the Event log.
However, the question is what you want to achieve? The macro will be resolved only in the admin UI - meaning that if there is an editor who has the preferred UI culture set to DE, then the string will be translated. It has no impact on the live site as the actual value saved into the DB is the "1" in this example. So, in your front end app you need to add logic to display appropriate translation for each value.