Not all viewers will be unable to understand the source. On a few occasions where another newspaper cited a German source and linked to it, I was able to determine that the original German article had simply been misinterpreted. Chinese speakers could do the same for sources in Chinese. Obfuscating sources just makes it harder to find out about such translation mistakes.

Second, even readers who do not understand the source themselves might need to know some specific detail contained therein (e.g. your company operates in China and you want to know how you might be affected). They could hire a professional translator to help them understand it.

The reason Reuters (and most other news sites) don't link to sources is probably that they don't want traffic to leave their site. They'll happily link to tangentially related articles on their own site, though.