Fawlty, since nobody searches for "widgets deutsch" or "widgets de" it doesn't matter at all. If you want to take a possible ranking advantage from having a keyword in the path, then you should use a keyword people are searching for.
If it's about the SE recognizing the page as being in german language the file name is irrelevant. SEs use automatic language detection. If you want to make sure to help the SE you should put in a meta lang tag.