I'm not sure that's the "right" sub to ask that, in the way that I don't see how to provide an historical answer.

As a non-english-native speaker, I tend to be hesitant like you when it comes to find sources for some research. I always try to consider different elements :

Does it concern something of your own country? If yes, maybe your native-tongue which usually evolved from the contemporary language used might be a better fit to reflect a contemporary viewpoint of the event. I tend to be frustrated to read in English some things that concern my home region/country seeing the lack of cultural grasp or the "lost in translation" parts. For example if you translate a word from Swedish to English you might lose some of its abstract concept with it (the idea that word convey a gender, a strength, an emotion).
However, sometimes it's interesting to have a different viewpoint in order to get away from our natural biased due to History, National pride...

If it doesn't concern your own country, then the same can be applied the other way around, but also could even concern a country that's neither yours nor a country that speaks a language that you know, and then it's very interesting to have different idea, with one text, you get multiple views because of the translation, thus you end up with a sort of debate within the text itself making you build a unique view and idea of the subject.

Other consideration is for whom you're doing the research? If it's for someone that does not speak the native language, you might want to consider to use a source that they can understand to provide more credits to your argument (but not exclusively!). When writing, and as any other kind of channel use in communication, always now your audience. To get your idea through, you need to talk/write in a way that will appeal to the receiver of the communication : they need to understand you, not only your words but also your references (pop culture, sources, media...).

Personally, I tend to always run to sources in my native tongue primarily since I'll always understand better the subtleties of my own language (I mean, in French, the choice of the word for "to say" could have an impact on the emotion behind it, like other languages), and I'll try to find something that could be in English to let more people to go through my sources and get lost on the Internet looking for more information.

I don't know if I helped you, I feel like I put even more confusion into your mind haha, sorry. Hopefully it will help you in some ways :).