Really, it is worth learning another language just for that! If you have a closer look at the references sections of most of my articles, you will find German and English references all together.
One great advantage of foreign sources is that there is literally no risk of accidentally copying the source. You see, to copy it, you would have to translate it. It is far easier to phrase the information you read in your own words, believe me.
Only take care that you don't name foreign resources for your "Further Reading" section ... your readers might just get it wrong ...
Ok, to make it easy for you to weight this:
- a lot more information at your disposal
- no risk of copying by accident
- need to be able to read the second language fluently or nearly fluently
- might need a good dictionary too
As you need a sound command of the second language, this might not be a valid option for those who just studied a second language for a year in college and almost forgot about it in the meantime. If someone has more than one first language, though, there is no reason why he shouldn't use this to his advantage.
For all others, this might be a motivation to improve a second language to a level where they can read and use information for their articles. Acquisiton of passive knowledge (which means you are able to understand but not to use it on your own) is far easier than acquisition of active knowledge. Plus: your passive knowledge will become active knowledge if used often enough. Thus, you can even kill two birds with one stone!
If you don't know if your editor would approve of sources in foreign languages, just ask. Or, like I did, just use your sources and wait whether someone complains or not. In my case, no one complained.